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UNIVERSITY  OF  CALIFORNIA 
AT    LOS  ANGELES 


GIFT  OF 

Thomas  W.   Hamilton,    Jr 


Practical        * 
Stamp-Milling  and 
Amalgamation 


BY 

H.  W.  MAcFARREN 

Author  of 

"Textbook  of  Cyanide  Practice11. 
'•Mining  Law  for  the  Prospector,  Miner ,  and  Engineer 


THIRD  EDITION 


WITH  A  CHAPTER  ON 

ARRANGEMENT  AND   CONSTRUCTION 
COSTS  OF  STAMP-MILLS 

By 
CHARLES  T.  HUTCHINSON 


PUBLISHED  BY  THE 

MINING  AND  SCIENTIFIC  PRESS,  SAN  FRANCISCO 

LONDON:  THE  MINING  MAGAZINE 
1914 

(Printed  in  U.  S.  A.) 


COPYRIGHTED  1914 

BY 
DEWEY  PUBLISHING  COMPANY. 


19  \A- 
PREFACE 


When  I  first  engaged  in  stamp-milling  and  amalgamation,  like 
many  others  I  eagerly  and  unsuccessfully  sought  for  a  treatise  that 
would  tell  me  what  to  do  and  why  —  that  would  give  the  ideas 
and  principles  by  which  millmen  were  to  be  guided,  and  the  methods 
found  to  be  most  satisfactory.  Later  the  subject  of  examining  ores 
and  the  adjusting  of  the  stamp-mill  to  their  requirements  became  of 
interest.  The  first  edition  of  this  book  incorporated  my  experience 
and  conclusions  along  the  above  lines,  and  the  knowledge  gathered 
from  other  millmen  and  metallurgists  with  whom  I  had  associated. 

Since  then  I  have  been  engaged  in  many  widely  separated  parts 
of  the  metal-mining  regions  of  the  United  States,  and  have  had 
further  opportunity  to  observe  stamp-mill  practice  and  to  discuss 
the  subject  with  millmen  and  metallurgists.  During  this  time  I  have 
also  prepared  a  work  on  standard  cyanide  practice.  As  a  result 
the  third  edition  of  this  book  is  an  entire  revision  and  enlargement 
that  has  been  illustrated  with  77  carefully  selected  cuts  and  drawings. 

This  book  now  endeavors  to  set  forth  the  principles  and  practice 
of  stamp-milling  and  amalgamation  which  time  and  experience  have 
indicated  as  correct  and  best.  It  is  written  directly  from  the  stand- 
point of  the  working  stamp-millman  for  those  interested  in  the 
details  of  practical  operation  and  construction.  However,  it  gives 
consideration  to  fine-grinding  and  cyanidation  where  these  are 
touched  upon. 

Mr.  Charles  T.  Hutchinson  was  formerly  manager  of  the  mining 
machinery  department  of  the  Union  Iron  Works  and  later  for  the 
Joshua  Hendy  Iron  Works,  both  of  San  Francisco.  From  the  expe- 
rience gathered  during  the  construction  of  many  mills,  he  has  written 
the  part  on  Arrangement  and  Construction  Costs  of  Stamp-Mills. 
Mr.  Hutchinson  is  also  one  of  the  host  who  have  contributed  many 
valuable  ideas  and  much  information  that  has  been  finally  incor- 
porated  in  the  other  part  of  the  text. 

H.  W.  MACFARREN. 

Salt  Lake  City,  July  1,  1910  (First  Edition). 
San  Francisco,  October  1,  1914  (Third  Edition). 


TABLE  OF  CONTENTS 


PART  I— STAMP-MILLING 

CHAPTER  I 

Page. 

The  Stamp-Mill  9 

Location  and  Design  11 

Rock-breaker,  Grizzly,  and  Ore-bin  14 

Battery-frame  and  Line-shaft    24 

Mortar-block 27 

CHAPTER  II 

Mortar  and  Mortar  Liner   34 

Shoe  and  Die 40 

Bosshead   45 

Tappet 46 

Cam    50 

CHAPTER  III 

Stem  and  Stem  Breakage 53 

Fastening  the  Stem  56 

Adjusting  Height  of  Drop    60 

Cam  Shaft  and  Cam-shaft  Box   61 

Order  of  Drop    65 

Stem  Guide   67 

Finger  Jack  68 

Feeder   69 

Screen    72 

CHAPTER  IV 

Water  Supply    84 

Principles  of  Stamp  Crushing  86 

Height  and  Speed  of  Drop  87 

Weight  of  Stamp  90 

Height  of  Discharge   97 

Feeding  the  Mortar  98 

Power 99 

Individual    Stamp    .  101 


PART  II— AMALGAMATION 


CHAPTER  V 

Properties  and  Care  of  Mercury   107 

Principles  of  Amalgamation  109 

Inside  Amalgamating  Plates   , .  110 


6  TABLE  OF  CONTENTS 

CHAPTER  VI 

Page. 

Splash  and  Lip-Plates   114 

Apron-Plate    116 

Dressing  and  Care  of  Apron-Plate  118 

Feeding  Mercury   122 

Dry  Amalgamation    124 

Outside  Amalgamation  125 

Amalgamation  in  Cyanide  Solution  127 

Water  Required  in  Amalgamation  128 

Temperature  of  Battery  Water 130 

Period  Between  Plate  Dressing 131 

CHAPTER  VII 

Construction  and  Arrangement  of  Apron  Table   132 

Accessories  to  the  Apron  Table   134 

Plates  Away  from  Mortar  136 

Silvered  or  Raw  Copper  Plates  and  their  Handling 137 

Recovering  Gold  from  Old  Plates  139 

Chemicals  and  their  Use  140 

Unsatisfactory  Bare  and  Hard  Plates 142 

Cleaning  Amalgam  and  the  Clean-Up 144 

CHAPTER  VIII 

Retorting  and  Percentage  of  Metal  in  Amalgam  150 

Melting  and  Sampling  Bullion   152 

Recovering  Gold  from  Slag,  Old  Screens,  Etc 156 

PART  III— GENERAL 

CHAPTER  IX 

Loss  of  Gold  in  Amalgamation  and  Its  Remedies  161 

Sizing  and  Mill  Tests  165 

Sampling     169 

Milling  Systems   170 

CHAPTER  X 

Millmen  and  Mill  Crews  176 

Mill  Management  181 

Handling  Pulp  and  Tailing  185 

PART  IV— ARRANGEMENT  AND  CONSTRUCTION  COSTS  OF 
STAMP-MILLS 

By  CHARLES  T.  HUTCHINSON 

CHAPTER  XI 

Arrangement  of  Stamp  Battery   191 

Light  and  Heavy  Stamps 195 

Sectionalized  Machinery    , 198 

Jaw  and  Gyratory  Crushers   202 

Purchasing  a  Mill   206 

Selection  of  Millsite   210 

Cost  of  Constructing  Stamp-Mills  . .   211 


PART  I 

STAMP- MILLING 


CHAPTER  I 

THE  STAMP-MILL — LOCATION  AND  DESIGN — ROCK-BREAKER,  GRIZZLY, 
AND  ORE-BIN — BATTERY  FRAME  AND  LINE  SHAFT — MORTAR- 
BLOCK. 

The  Stamp-Mill. — The  supremacy  of  the  stamp-mill  for  crushing 
gold  and  silver  ores  and  the  reason  why  it  has  so  successfully  with- 
stood the  attempts  of  both  theoretical  and  practical  men  to  super- 
sede it  or  limit  its  application,  lie  mainly  in  its  simplicity,  reliability, 
and  wide  range  of  adaptability.  The  modern  gravity-stamp  has 
been  evolved  from  the  mortar  and  pestle  used  by  primitive  man, 
and  has  remained  simple  in  principle  and  construction. 

At  first  sight  it  appears  to  be  a  crude  machine.  All  is  done  by 
gravity.  There  is  an  absence  of  the  elevating,  conveying,  and  re- 
working, which  give  so  much  trouble  in  the  other  systems  of  milling. 
Its  range  of  adaptability  is  far  greater  than  that  of  any  other 
crusher.  It  is  used  in  Gilpin  county,  Colorado,  in  the  treatment  of 
a  gold  ore  slow  to  amalgamate,  with  its  crushing  capacity  subordi- 
nated in  the  effort  to  give  the  ore  the  particular  treatment  required 
to  save  the  gold,  the  daily  output  being  reduced  to  one  ton  per 
stamp.  In  South  African  practice  amalgamation  is  subordinated  to 
crushing,  resulting  in  a  daily  capacity  as  high  as  ten  to  twenty  tons 
per  stamp.  The  stamp  is  used  for  disintegrating  cemented  gold- 
bearing  gravel  and  for  pulverizing  the  softest  rock,  as  well  as  for 
crushing  the  hardest  and  toughest  quartz.  It  may  be  fed  with  fine 
material  having  only  sufficient  grit  to  keep  the  shoes  from  hammer- 
ing the  dies,  up  to  slabs  of  rock  the  size  of  a  large  meat-platter  and 
3  to  4  in.  thick.  Such  rock  is  often  sent  through  the  battery  during 
a  break-down  of  the  rock-crusher.  It  will  crush  wet  or  dry.  It 
will  deliver  its  product  through  a  4  or  a  40-mesh  screen,  or  through 
a  still  finer  one  if  desired,  though  the  modern  stamp-battery  is  not 
adapted  to  crushing  to  advantage  through  a  screen  finer  than  40- 
mesh.  No  machine  can  compare  with  it  in  amalgamating,  or  in  pre- 
paring an  ore  for  concentration,  except  where  the  extremely  friable 
nature  of  the  material  requires  stage-crushing;  yet  it  has  made 
an  enviable  record  in  crushing  and  preparing  pyritic  copper  ore  for 
the  concentration  of  its  sulphide.  In  the  hands  of  a  metallurgist 
who  has  made  a  study  of  the  stamp-mill,  a  great  diversity  of  treat- 
ment can  be  given  an  ore  in  an  experimental  way,  to  ascertain  the 
best  for  adoption  in  that  particular  case. 

9 


10  SUPERIORITY   OF   STAMP-MILL 

The  stamp-mill  stands  in  a  class  by  itself  by  reason  of  the  variety 
of  ores  that  may  be  treated,  the  widely  varying  methods  that  may 
be  employed  or  the  products  obtained,  and  the  control  over  opera- 
tions to  effect  any  reasonable  end,  all  without  reconstruction,  re- 
modeling, or  material  delay  or  change,  but  mainly  by  adjustments 
which  are  a  part  of  the  daily  routine. 

Estimates  of  the  tonnage  and  costs  with  a  stamp-mill  can  be 
made  in  advance  with  a  close  approximation  to  exactness.  So  thor- 
oughly can  it  be  depended  upon  that  it  has  passed  into  an  axiom 
that  a  standard  stamp-mill  has  never  caused  the  closing  of  a  prop- 
erty by  failing  to  do  good  work  where  good  work  was  possible,  and 
that  it  has  replaced  to  advantage,  at  some  time  or  other,  practically 
every  other  kind  of  crushing  machine.  It  is  true  that  there  are 
stamp-mills  that  are  incapable  of  good  work,  due  to  careless  manu- 
facture, to  incompetent  mill-wrighting,  and  to  imprudent  economiz- 
ing on  the  part  of  the  mining  company;  but  despite  this  the  average 
millman  manages  to  treat  a  fair  tonnage  and  to  make  a  good  ex- 
traction with  them,  so  that  the  president  of  the  company  in  his  city 
office  is  often  unaware  that  his  mill  is  not  up  to  the  standard. 

The  opponents  of  the  stamp-mill  present  elaborate  statements 
showing  that  the  cost  of  installation  and  the  power  consumed  ex- 
ceeds that  of  other  processes.  This  is  true  in  certain  cases,  but  they 
are  only  theoretical  statements  and  when  tested  out  in  actual  prac- 
tice too  often  show  the  balance  to  be  in  favor  of  the  stamp-mill.  But 
where  the  cost  of  installation  and  the  power  consumed  by  the  stamp- 
mill  are  greater,  it  "is  found,  almost  without  exception,  that  the 
stamp-mill  has  other  points  of  superiority  that  outweigh  these 
disadvantages.  The  principal  stock  argument  against  the  stamp- 
mill  is  the  abnormal  amount  of  power  it  is  reputed  to  require.  A 
careful  examination  and  comparison  of  individual  cases  in  actual 
practice  show  this  increase  to  be  small  or  trifling  in  cost  per  ton  of 
ore  crushed,  and  that  the  other  advantages  of  the  stamp-mill  are  so 
great  that  any  increased  power  cost  sinks  into  insignificance. 

It  must  be  remembered  that  exact  and  correct  data  of  what  a 
stamp-mill  will  do  can  be  compiled,  but  that  the  advance  estimates 
of  what  other  processes  and  devices  will  attain  is  seldom  realized 
under  normal  conditions.  It  is  in  the  lower  cost  of  operating  and 
repairing,  less  loss  of  operating  time,  and  wider  range  of  treatment 
at  command,  that  the  stamp-mill  overshadows  all  other  crushing 
machines  and  processes. 

It  is  an  object  lesson  to  go  into  some  of  the  large  and  small  mills 
that  stud  the  Mother  Lode  of  California  so  closely  that  he  who 


LOCATION   OF   MILL  11 

travels  through  the  counties  of  Amador,  Calaveras,  and  Tuolumne, 
is  seldom  out  of  hearing  of  their  roar ;  to  note  the  ease  with  which 
the  ore  by  gravity  runs  through  the  mill,  the  little  labor  necessary, 
the  cleanliness  of  the  place,  and  the  smallness  of  the  scrap  pile, 
consisting  mainly  of  worn-out  shoes,  dies,  and  screens ;  and  then  to 
go  to  a  wet-roll  or  dry-process  mill  with  sloppy,  muddy  floors,  or 
dust-covered  machinery,  jammed  rolls,  elevators  out  of  order,  a 
small  army  of  mechanics  and  helpers  on  construction  and  repairs, 
and  a  mountainous  scrap-pile  of  broken  and  worn-out  machinery. 

Location  and  Design. — The  selection  of  a  mill-site  is  in  some  cases 
a  simple  matter,  in  others  it  is  complicated  by  so  many  factors  as  to 
be  a  most  difficult  problem.  Erecting  the  mill  some  distance  away 
when  it  could  have  been  built  to  advantage  near  the  mine,  is  one 
of  the  most  common  mistakes.  Operations  should  be  centralized 
and  concentrated  as  much  as  possible.  Two  operating  points,  with 
much  of  their  equipment  in  duplicate,  increases  the  working  costs. 
The  great  cost  of  installing  and  repairing  transportation  lines  and 
systems  is  often  overlooked  in  making  estimates  of  working  costs. 
Another  common  mistake  is  the  hauling  of  ore  a  long  distance  to 
water,  when  water  could  be  obtained  close  at  hand  by  a  little 
development,  or  by  further  sinking  in  the  mine  if  the  mine  water  is 
suited  to  amalgamation — in  a  few  cases  it  has  not  been.  Three 
observations  may  be  made :  first,  that  it  is  easier  to  transport  water 
to  ore,  than  ore  to  water.  Second,  that  usually  more  water  is 
developed  in  a  mine  by  sinking  than  is  generally  anticipated  before 
the  workings  have  attained  much  distance  from  the  surface.  Third, 
that  the  increasing  perfection  of  machinery  and  systems  for  dewater- 
ing  and  conveying  mill  tailing  has  made  it  less  and  less  advisable  to 
separate  the  mill  from  the  mine  on  account  of  small  water  supply 
at  the  mine. 

Where  ore  is  supplied  to  a  large  mill  by  an  aerial  tramway,  an 
attempt  should  be  made  to  place  the  mill  so  that  the  cable  may  run 
lengthwise  over  the  bin,  enabling  the  buckets  to  be  tripped  at  any 
point,  thus  dispensing  with  a  belt-conveyor.  It  can  be  arranged  to 
have  the  buckets  dump  directly  onto  a  gyratory  breaker.  In  some 
cases  the  aerial  tramway  has  supplied  the  power  to  run  the  breaker. 
With  a  mill  adjacent  to  a  working  adit,  straight  tracks  and  heavy, 
well-ballasted  rails  will  enable  large  cars — three  tons — to  be  used 
with  ease.  At  a  shaft-mine  it  is  well  to  place  the  mill  near  the  hoist 
when  possible.  Hoisting  may  then  be  done  by  self-dumping  skips 
into  an  ore-bin  from  which  the  ore  may  run  by  gravity  to  one 
breaker  for  a  20-stamp  mill,  to  two  breakers,  one  on  each  side  of 


12 


DESIGN   OP  MILL 


the  bin,  for  a  40-stamp  mill,  or  through  one  rock-breaking  system 
connected  by  belt-conveyor  to  more  than  40  stamps.  The  objection 
to  putting  the  mill  and  hoist  together  is  that  in  event  of  fire,  both 
will  probably  be  burned,  and  the  fire  communicated  to  the  shaft 
timbers. 

Efforts  should  be  made  to  dispense  with  elevators  of  any  nature 
for  both  wet  and  dry  material,  and  to  a  lesser  extent  with  belt-con- 


INCLINE    SHAFT    WITH    SELF-DUMPING    SKIP   HOISTING    ORK   DIRECTLY    INTO    MILL   AND 
WASTE  INTO  BIN  FOB  TRAMMING  TO  DUMP. 

veyors.  A  large  part  of  the  advantage  from  using  the  stamp-battery 
is  due  to  the  absence  of  elevating  and  conveying  machinery.  Extra 
expense  to  secure  greater  simplicity  is  money  well  spent.  The 
stamp-battery  is  an  ideal  illustration  of  the  'unit  idea'  in  con- 
struction as  well  as  in  operation,  and  a  mill  should  be  so  situated 
that  it  can  be  added  to,  though  the  proportion  of  mills  that  are  in- 
creased in  size  is  small. 

The  roof  of  the  mill  should  not  be  in  one  solid  sheet,  but  should 
be  broken  by  drops  at  the  different  floors,  that  the  various  floors 
may  be  well  lighted  by  windows  set  in  these  drops. 

There  are  several  excellent  reasons  for  painting  the  interior  of 
the  mill  white.  It  causes  the  employees  to  keep  the  mill  neater  and 
cleaner.  It  greatly  increases  the  light,  perhaps  nearly  doubling  it, 


LAW   OF    MILLSITE   LOCATION  13 

and  tends  to  eliminate  dark  corners.    The  coating  of  paint  is  to  some 
extent  a  protection  against  fire. 

It  should  be  possible  to  reach  the  head  and  foot  of  the  mill  by 
wagon;  also  to  unload  shoes  and  dies  at  the  plate-floor,  and  stems 
and  other  parts  at  the  cam-floor.  Likewise,  the  location  of  the 
machine  shop  in  its  relationship  to  the  mill  should  be  carefully 
planned. 

Where  it  is  necessary  to  set  a  water-wheel  so  low  that  it  may  be 
in  danger  during  high  water,  in  the  effort  to  secure  higher  head, 
the  mill  may  be  set  higher  up,  out  of  the  danger  zone,  and  connected 
with  the  water-wheel  by  a  rope-drive. 

The  disposal  of  the  tailing  should  be  carefully  considered,  and 
the  title  or  irrevocable  right  to  ground  on  which  it  can  be  dumped 
should  be  secured,  even  if  it  does  not  appear  that  this  ground  will 
be  needed,  for  a  trespassing  tailing,  like  smelter-fume,  can  be  made 
a  basis  for  damage  suits.  It  is  not  necessary  to  build  the  mill 
adjoining  a  good  site  for  impounding  the  tailing,  or  an  existing 
cyanide  plant.  The  tailing  can  be  ditched,  piped,  or  flumed  a  long 
distance.  Concentrate  has  been  conducted  in  pipes  as  small  as  one 
inch  in  diameter  down  mountain  sides  and  across  rivers  to  reduction 
works  and  storage  bins. 

The  mining  laws  of  the  United  States  allow  non-mineral  land  to 
be  located  and  patented  as  millsite  claims  of  five  acres  each,  for 
milling  purposes  or  any  uses  connected  with  the  development  of 
mining  claims,  without  the  necessity  of  annual  labor  or  development 
work  upon  the  millsite — though  necessary  upon  the  lode  claim  to 
which  the  millsite  is  attached.  This  is  an  excellent  method  of 
obtaining  land  for  mills,  camp  sites,  pumping  plants,  dumping  tail- 
ing, storing  ore,  etc.  Work  or  care  on  or  in  a  mill  will  not  answer 
for  annual  labor  or  assessment  work  or  for  the  development  work 
required  for  patent  purposes.  As  mining  locations  can  easily  be 
lost  or  forfeited  if  unpatented,  mills  should  never  be  placed  upon 
unpatented  land.  There  is  a  separate  and  distinct  law  which  per- 
mits the  owner  of  a  mill  or  reduction  works  to  secure  patent  on  his 
millsite  without  the  necessity  of  development  work  and  without  the 
millsite  being  associated  with  a  lode  claim;  this  law  is  especially 
applicable  to  custom  mills.* 

"The  mining  laws  of  the  United  States  relative  to  millsites,  to  water  rights 
for  mining  and  milling  purposes,  and  to  the  use  of  timber  from  government 
land  for  mining  and  milling  purposes  are  fully  explained  in  Chapters  12, 
26,  and  28  of  'Mining  Law  for  the  Prospector,  Miner,  and  Engineer,'  by  the 
Author. 


14  JAW   VS.    GYRATORY   ROCK-BREAKERS 

Rock-Breaker,  Grizzly,  and  Ore-Bin. — Rock-breakers  for  stamp- 
mill  work  are  of  two  types,  the  Blake  jaw-crusher  and  the  gyratory 
crusher.  Each  of  these  breakers  has  characteristics  which  fit  it  for 
certain  conditions,  but  both  types  give  satisfactory  service  under 
widely  varying  conditions.  The  Blake  jaw-crusher  requires  much 
less  mill  height  and  less  overhead  space  for  repairing.  It  requires 
less  repairing,  and  it  is  more  easily  performed.  For  these  reasons 
the  Blake  crusher  is  suited  to  small  installations,  especially  those 
where  first  cost  is  to  be  kept  low,  also  where  good  mechanics  may 
not  be  available.  The  cost  of  the  Blake  is  less  for  capacities  under 
20  tons  per  hour,  while  the  gyratory  is  cheaper  in  first  cost  for 
greater  capacities.  The  jaw-crushers  have  rectangular  openings 
which  are  well  proportioned  to  enable  them  to  receive  very  coarse 
rock  or  boulders.  The  openings  of  the  gyratory  are  comparatively 
narrow,  so  that  a  great  deal  of  sledging  or  hand-breaking  of  the 
coarse  rock  and  boulders  must  be  done.  Gyratory  breakers  with 
large  openings  for  big  boulders  can  be  built,  but  they  are  of  such 
enormous  size  and  capacity  that  they  are  only  suited  to  mills  of 
tremendous  tonnage.  This  is  the  reason  that  so  many  large  two- 
stage  breaking  plants  are  using  jaw-crushers  for  the  preliminary 
breaking.  The  gyratory  produces  a  more  even  product,  also  a 
larger  amount  of  fine  material  through  its  grinding  effect.  For  the 
latter  reason,  jaw-crushers  are  preferable  for  preliminary  breaking 
where  ore-sorting  is  to  follow.  The  jaw-crusher  is  superior  for 
breaking  wet  ore.  The  gyratory  requires  less  care  in  feeding  and 
the  ore  may  be  dumped  directly  upon  it.  This  fits  it  for  certain 
places,  such  as  where  tramway  buckets  or  mine  cars  empty  upon 
it,  and  also  makes  feeding  by  automatic  feeders  easier  than  with 
the  Blake  type.  The  gyratory  is  used  almost  exclusively  as  the 
secondary  or  final  fine-crushing  breaker  in  two-stage  breaking. 
Under  conditions  favorable  to  it,  the  gyratory  is  cheaper  in  first 
cost,  power,  repairs,  and  labor.  In  selecting  the  breaker  and  break- 
ing system  to  be  used,  the  size  of  the  ore  that  the  mine  will  supply 
should  be  considered,  in  addition  to  a  multitude  of  other  things. 

The  common  practice  in  rock-breaking  is  to  use  a  Blake  jaw- 
crusher  for  10  stamps,  a  Blake  or  gyratory  for  20  stamps,  or  two 
for  40  stamps  when  the  breakers  are  located  over  the  mill  bins,  as 
one  breaker  cannot  readily  spread  ore  to  more  than  20  stamps.  A 
single  rock-breaking  unit,  with  means  for  conveying  the  broken 
ore,  is  frequently  used  for  40  stamps.  Such  a  unit  may  consist  of 
one  large  gyratory,  which  should  be  preceded  by  a  grizzly  to  screen 
out  the  fine  ore  if  the  gyratory  is  to  be  run  at  its  utmost  capacity. 


ROCK-BREAKER   ARRANGEMENT 


15 


If  a  large  gyratory  is  used  so  that  the  wider  openings  may  receive 
the  larger  lumps  of  ore  without  sledging,  the  capacity  will  be  so 
large  that  the  grizzly  may  be  dispensed  with.  A  grizzly  must  be 
used  if  the  ore  comes  wet  from  the  mine,  as  no  breaker  works  well 
when  jammed  with  fine  wet  material.  It  may  be  advisable  with  40 


BLAKE    JAW-CKUSHEB    WITH    SOLID    FRAME. 

(Colorado  Iron  Works  Co.,  Denver,  Colo.) 


stamps,  and  always  with  more,  to  practise  two-stage  rock-breaking 
by  breaking  coarsely  in  a  preliminary  breaker,  followed  by  screen- 
ing and  re-breaking  the  oversize  in  smaller  breakers.  This  is  be- 
cause of  the  difficulty  of  reducing  a  large  amount  of  coarse  ore  to 
a  fine  product  in  one  breaker,  even  though  the  breaker  is  large  in 
size;  the  point  being  that  the  larger  parts  of  the  large  breakers 
must  necessarily  have  a  greater  movement,  which  results  in  the 
openings  being  much  wider  when  at  a  maximum  and  the  passing 
of  much  coarsely  broken  rock.  The  preliminary  breaking  is  per- 
formed in  a  Blake  or  gyratory — often  a  large  gyratory  without  a 
grizzly — the  ore  thence  passing  through  a  revolving  screen  or  trom- 
mel which  delivers  the  oversize  to  one  or  two  small  fine-breaking 


16 


ROCK-BREAKER   ARRANGEMENT 


gyratories.  The  product  is  delivered  to  a  belt-conveyor,  if  the 
crusher  building  is  adjacent  to  the  mill,  for  distribution  to  the  mill 
bins,  or  it  is  dropped  into  a  storage  bin  for  conveyance  by  other 
means. 

The  breaker  should  be  driven  by  separate  power  that  it  may  in 
no  way  interfere  with  the  running  of  the  stamps,  especially  with 
stamps  driven  by  water  power.  It  should  be  enclosed  from  the  bal- 


BLAKE   JAW-CRUSHER   WITH    SECTIOXAL   FRAME   TIED   TOGETHER  WITH    STKKI,    RODS. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 


ance  of  the  mill  that  the  dust  may  be  kept  out  of  the  bearings  and 
machinery  below.  A  grizzly  should  always  precede  jaw-crushers. 
It  is  generally  best  to  have  a  grizzly  precede  a  gyratory  crusher 
that  it  may  operate  to  its  full  capacity,  also  that  it  may  not  become 
jammed  through  an  excess  of  fine  material  and  thereby  break  a 
pinion.  Some  consider  that  dispensing  with  the  grizzly  decreases 
the  wear  on  the  crushing  faces  of  the  gyratory.  Short  grizzlies  of 
6  or  8  ft.  length  will  do  where  the  ore  passes  over  them  in  a  thin, 
constant  stream,  as  from  the  bin  to  the  breaker.  Where  the  ore  is 
dumped  intermittently  upon  the  grizzly  in  large  quantities,  the 
grizzly  should  be  quite  long.  Trommels  screen  more  accurately 
than  grizzlies,  especially  in  finer  screening,  but  require  power,  are 


GRIZZLY 


17 


GYRATORY    CRUSHER. 

(Austin  Mfg.  Co.,  Chicago.) 


SECTION  OF   GYRATORY   CRUSHER. 

(Austin  Mfg.  Co.,  Chicago.) 


IS 


AUTOMATIC   FEEDER   FOR   ROCK-BREAKER 


more  costly  in  first  cost  and  repairs,  and  require  a  light,  continuous 
feed. 

Belt-driven  plunger  or  metal  belt-conveyor  feeders  of  a  size  able 
to  handle  coarse  rock  are  in  use  in  concentrating  mills  for  feeding 
breakers,  even  breakers  of  the  jaw  type;  and  as  they  enable  the 
breakers  to  be  fed  automatically,  they  may  be  expected  to  become 
a  detail  of  stamp-mill  equipment. 

Electro-magnets  are  suspended  over  conveyor  belts  to  pick  up 
hammer  heads,  broken  drill  steel,  and  other  iron  and  steel,  so  that 
they  may  not  pass  into  the  breaker  and  crushing  apparatus. 


REVOLVING   ROCK   SCREEN   OR  TROMMEL. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 


Many  small  mills  are  built  in  which  it  is  necessary  for  the 
breakerman  to  shovel  or  scrape  into  the  breaker  every  pound  of 
ore  that  passes  through  it.  If  sufficient  height  be  not  available  for 
placing  a  crude-ore  bin  above  the  breaker,  then  a  gyratory  breaker 
preceded  by  a  grizzly  should  be  used,  and  the  ore  should  be  dumped 
directly  upon  the  breaker.  This  method  of  dumping  directly  and 
dispensing  with  a  breakerman  will  not  be  successful  with  a  wet, 
sticky  ore  that  'balls  up'  in  the  breaker,  nor  where  the  ore-supply 
does  not  come  in  small  lots,  although  the  breaker  may  be  buried 
with  a  dry,  brittle  ore  having  no  lumps  too  large  to  enter  the  jaws. 

Where  it  is  not  desired  to  dump  directly  upon  the  breaker,  a 


ORE-BIN   ARRANGEMENT 


crude-ore  bin  should  be  used.    This  need  not  have  a  sloping  bottom, 
for  should  the  supply  run  low,  the  breakerman  can  enter  the  bin 


FORWARD. 
RECIPROCATING  PLATE  FEEDER. 
(Stephens-Adamson  Mfg.   Co.,   Aurora,   111.) 


and  shovel  the  ore  forward.  The  grizzly  should  follow  this  bin, 
emptying  directly  into  the  crusher.  An  apron  underneath  the 
grizzly  should  carry  the  fine  ore  that  has  passed  the  grizzly  bars  to 


THE  S-A  STEEL  APRON  FEEDER. 

(Stephens-Adamson   Mfg.   Co.,  Aurora,   111.) 


the  point  where  the  breaker  discharges,  that  the  coarse  and  fine 
ore  may  be  well  mixed.  The  placing  of  the  grizzly  before  the  crude- 
ore  bin  where  the  ore  from  the  mine  is  dumped  directly  upon  it, 


20  ORE-BIN    ARRANGEMENT 

and  the  fine  ore  shunted  by  the  cnide-ore  bin,  or  any  construction 
that  tends  to  keep  the  ore  in  the  crushed-ore  bin  from  being  homo- 
geneous, is  bad  and  must  be  condemned.  The  height  of  drop  of 
the  stamps  in  a  battery,  and  the  other  adjustments,  are  made  for 
each  ore  mainly  according  to  its  character,  hardness,  and  fineness. 
Where  the  mill  arrangement  is  such  that  the  fine  and  coarse  ore 
delivered  to  the  mill  during  the  day  become  segregated,  a  hard, 
coarse  rock  from  the  breaker  is  at  first  fed  to  the  mortars,  and  the 
mill  works  splendidly  during  the  day  and  early  evening;  but  late 
in  the  evening,  the  coarse  rock  in  the  front  part  of  the  bin  being 
exhausted,  the  fine  from  the  grizzly  begins  to  come.  The  stamps 


PLUNGER  ORE  FEEDER  FOR  CRUSHERS,  ETC. 

(Chalmers  &  Williams,  Chicago  Heights,  111.) 

having  a  long  drop  for  the  hard,  coarse  rock,  now  sink  through  this 
fine  ore  and  strike  the  dies,  and  from  then  on  the  millman  has 
trouble.  While  the  stamp-battery  can  be  adjusted  to  work  well 
on  this  fine  material,  it  is  obvious  that  such  adjustments  for  the 
two  classes  of  ore  cannot  be  made  economically  twice  daily.  Be- 
sides the  trouble  in  feeding,  there  is  danger  in  the  'camming'  of 
the  stamps  that  break  through  the  bed  of  pulp  to  the  die — the  fall- 
ing stamp,  through  its  longer  drop,  being  arrested  by  the  tappet 
falling  on  the  cam  instead  of  the  shoe  being  cushioned  on  the  coarse 
ore  over  the  die.  This  fine  rock  is  usually  many  times  richer  than 
the  coarse,  and  the  millman,  engrossed  in  other  troubles,  may  fail 
to  feed  the  additional  quicksilver  or  make  the  extra  dressings  of 
the  plates  that  may  be  required. 

The   crushed-ore  bin,   in  fact  any   bin  supplying   an  automatic 
feeder,  should  have  a  sloping  bottom  of  from  40  to  50°.    The  only 


SLOPING   VS.    FLAT-BOTTOM    BINS 


21 


real  argument  in  favor  of  the  flat-bottom  bin  is  that  it  gives  a  re- 
serve ore-supply,  but  this  reserve  might  as  well  be  outside  the  mill, 
except  in  the  case  of  accident  to  the  breaker,  for  it  will  all  have  to 
be  shoveled.  It  has  been  said  that  this  extra  ore  by  its  weight 
anchors  the  bin  and  adjacent  parts  of  the  mill.  The  reply  to  this 
is  that  a  well-constructed  mill  does  not  require  such  anchoring. 


SIDE  ELEVATION    OF    STAMP-MILL. 

(Traylor  Engineering  &  Manufacturing  Co.,  Allentown,  Pa.)  * 

Many  arguments  and  sophistries  are  advanced  that  these  flat-bottom 
bins  will  be  kept  full  and  that  no  shoveling  will  be  required;  but 
actual  observation  shows  that  they  are  not  kept  full,  and  that 
occasional  shoveling  must  be  done.  This  requires  an  extra  man  or 
extra  men,  and  the  charges  for  this  item  soon  amount  to  15  to  30c. 
per  ton.  If  a  millman  has  to  go  into  the  bin,  he  gets  surly,  and 


ZZ  ORE-BIN    CONSTRUCTION 

voluntarily  or  involuntarily  neglects  his  other  work.  A  sloping 
bottom  is  advantageous  where  a  wet,  fine  ore  that  will  neither  roll 
nor  run  is  being  milled,  such  as  'old  filling'  from  the  mine-stopes. 
By  introducing  a  few  pails  of  water  at  the  top  and  back  of  the  bin, 
the  whole  mass  can  be  started  moving  slowly  into  the  feed-chutes; 
care  must  be  exercised  in  the  amount  of  water  used,  or  the  whole 
mass  will  move  down  into  the  mortars  regardless  of  the  feeders, 
and  unless  the  stamps  are  immediately  hung  up,  the  screens  will  be 
broken  out;  in  either  case  the  excess  of  pulp  or  ore  will  have  to  be 
dug  out  of  the  mortars.  In  some  mills  1-in.  pipes  are  arranged  to 
deliver  a  constant  small  stream  of  water  upon  such  ore  at  the  chute 
between  the  bin  and  the  hopper  of  the  feeder.  A  water  spray  is 
sometimes  used  at  the  rock-breaker  to  lessen  the  dust. 

A  compromise  bin  where  the  sloping  bottom  begins  not  at  the 
feed-chute  door,  but  halfway  back  on  the  bin-sills,  does  not  give 
the  advantage  of  either  the  sloping  or  flat-bottom  bin.  The  bin 
should  have,  in  addition  to  its  double  planking,  steel  plates  at  the 
points  of  greatest  wear,  which  are  the  grizzly  apron,  the  point  where 
the  ore  drops  into  the  bin,  and  just  above  each  feed-chute  opening. 
Steel  rails,  usually  worn  ones  that  have  been  discarded,  are  used  in 
lieu  of  steel  plates  as  they  last  for  a  great  length  of  time,  whereas 
steel  plates  become  worn  in  the  course  of  time  and  break  and  curl 
up.  These  rails  also  make  excellent  grizzlies.  The  planking  of 
the  bottom  of  a  bin  and  the  grain  of  its  wood  should  be  lengthwise 
to  the  flow  or  movement  of  the  ore  to  lessen  the  wear,  reduce  the 
hindrance  to  the  sliding  and  rolling  of  the  ore,  and  to  enable  those 
parts  subject  to  excessive  wear  to  be  repaired  or  replaced  without 
removing  the  less  worn  planking.  The  lower  3  ft.  of  the  planking 
on  the  front  of  the  bin  should  be  placed  on  the  outside  of  the  bin- 
posts,  instead  of  inside,  as  the  remaining  planking.  This  will  per- 
mit the  millman  to  insert  a  bar  or  shovel  from  the  cam-floor  and 
to  start  the  ore  when  it  is  low  or  has  'bridged,'  or  it  will  enable 
him  easily  to  enter  the  bin ;  a  cover  of  canvas,  or  a  hinged  board, 
between  the  outside  and  inside  planking  will  keep  the  dust  back. 
With  bins  as  ordinarily  constructed,  it  is  well  to  bore  a  large  hole 
or  cut  a  small  square  opening  to  be  covered  with  a  secure  metal 
slide  cover,  at  a  point  a  few  feet  above  each  feed-chute;  this  will 
enable  a  steel  bar  to  be  inserted  from  the  cam-floor  for  starting  the 
ore  when  it  has  'bridged.' 

It  is  possible  to  increase  the  size  of  the  mill  by  taking  a  feed-chute 
out  of  the  corner  of  the  bin  and  at  an  angle  to  it,  to  another  5- 
stamp  battery  in  line  with  the  original  batteries.  One  side  of  the 


23 


rtc 


24 


BACK-KNEE   BATTERY-FRAME 


mill  is  always  free  to  make  such  an  addition,  while  the  other  will 
usually  require  some  change  in  the  driving  arrangements.  Where 
this  idea  is  kept  in  view  in  building  a  10-stamp  mill,  and  a  large 
high  bin  is  built,  it  will  be  possible  to  turn  it  into  a  20-stamp  mill 
easily  and  cheaply. 

Battery-Frame  and  Line-Shaft. — In  battery  construction,  the  back- 
knee  type,  where  the  battery-posts  are  tied  to  the  ore-bin,  and  the 
line-shaft  driving  the  cam-shafts  is  placed  on  the  streak-sills  under- 
neath the  feeder-floor,  is  now  given  the  preference.  This  style  re- 
quires the  least  amount  of  timber.  It  is  the  strongest  and  most  rigid 


STAMP-BATTERY  WITH   BACK-KNEE  FRAME  AND   CONCRETE   MORTAR-BLOCK. 

(Denver  Engineering  Works  Co.,  Denver,  Colo.) 


BATTERY-FRAME   AND   LINE-SHAFT 


25 


construction,  especially  in  view  of  the  belt  pull.  It  gives  a  clean- 
cut  and  well-lighted  mill,  with  the  upper  part  of  the  battery  and 
mill  in  sight  from  the  plate-floor.  The  objections  are  that  a  belt- 
tightener  must  be  used  on  the  battery  belts,  but  this  answers  for 
the  friction-clutch  with  which  the  pulleys  of  all  horizontal  battery 
belts  should  be  provided.  However,  the  wear  and  tear  on  these  belts 
is  much  greater  than  on  belts  not  requiring  tighteners.  It  has 
been  feared  that  tying  the  battery-posts  and  framing  to  the  ore-bin 
would  cause  them  to  be  thrown  out  of  line  by  settling  of  the  bin; 


FROXT-KXEE    TYPE   OF    BATTERY-FRAME. 


this  can  only  occur  with  bins  set  on  a  loose,  poor  foundation,  and 
has  seldom  given  any  trouble.  Placing  the  line-shaft  on  the  streak- 
sills  has  been  criticized  as  putting  it  in  a  place  hard  to  get  at  and 
subject  to  dirt  and  water.  Plenty  of  head-room  should  be  allowed 
between  the  streak-sills  and  the  feeder-floor,  that  the  shaft  may  be 
easily  reached  for  repair.  Drainage  should  likewise  be  provided. 
Ring  oilers  should  be  used  and  dust-caps  of  canvas  provided.  In  a 
well-constructed  mill,  no  water  will  reach  the  shaft.  The  placing 
of  the  line-shaft  on  the  bin-sills  in  the  rear  of  a  sloping-bottom  ore- 
bin  gives  all  the  advantages  of  the  style  previously  described,  with 
the  additional  one  that  the  belt  is  horizontal  and  requires  no 
tightener.  This  style  is  limited  to  20  stamps  as  the  battery  belts 


26  FRONT-KNEE   BATTERY-FRAME 

must  pass  on  the  outside  of  the  bin,  and  it  is  advisable  to  make  the 
bins  continuous.  The  back-knee  type  is  now  used  almost  exclusively 
in  modern  mills.  In  a  mill  of  40  stamps  or  more  there  should  be  at 
least  one  stairway  leading  from  the  foot  of  the  plates  on  the  plate- 
floor  to  the  front  of  the  cam-floor,  that  millmen  need  not  go  to  end 
of  mill  or  behind  mortars  to  ascend  to  the  cam-floor.  A  raised 
edge  of  1%  in.  should  surround  all  openings  on  the  cam-floor  that 
tools,  spilled  ore,  etc.,  may  not  be  jarred  off  the  floor.  Removable 


UPPER   PLATFOBM    OB   CAM-FLOOR   OF    FRONT-KNEE    TYPE    OF    BATTERY-FRAME. 

Cam-shaft  pulleys  are  belted  direct  to  back-geared  electric  motors  without  use 

of  line-shafts. 
(Steams-Roger  Mfg.  Co.,  Denver,  Colo.) 

hand  railings  should  surround  the  cam-pulleys,  belts,  and  all  open- 
ings for  the  safety  of  the  millmen. 

In  the  front-knee  type,  the  line-shaft  is  placed  on  a  level  with 
the  cam-shaft  and  in  front  of  it  on  heavy  timbers  that  form  a  part 
of  the  battery  framing  and  brace  it  independently  of  the  ore-bin, 
though  it  can  be  tied  to  the  bin.  It  requires  more  timber  and  is 
neither  as  strong  nor  as  steady  as  the  back-knee  type,  while  the  upper 
platform  darkens  the  mill  and  does  not  allow  the  upper  part  of  the 
mill  and  battery  to  be  seen  from  the  plate-floor.  It  is  not  suitable 


WOOD  VS.   CONCRETE  MORTAR-BLOCKS 


27 


for  10  stamps  unless  tied  to  the  bin,  as  the  tendency  of  the  battery 
is  to  sway  endwise  on  account  of  its  comparatively  small  area  of 
longitudinal  anchorage. 

Mortar  Block. — The  battery  foundation  or  mortar  block  is  one 
of  the  most  important  parts  of  a  stamp-mill.  These  blocks  were  of 
wood  until  recent  years,  when  concrete  mortar-blocks  have  come 
into  favor  to  such  an  extent  that  wooden  blocks  are  no  longer  placed 


STANDARD    TEN-STAMP   CALIFORNIA    STAMP-MILL   OF   BACK-KNEE   TYPE   WITH   WOOD 
MORTAR-BLOCKS. 

(Union  Iron  Works  Co.,  San  Francisco.) 

in  elaborately  designed  mills.  It  was  at  first  thought  that  the  con- 
crete blocks  caused  stems  and  cam-shafts  to  break  faster  than  with 
wood  blocks  because  there  was  no  cushioning  of  the  impact  and 
jar,  but  with  more  experience  it  has  been  positively  established  that 
where  the  block  has  been  built  and  the  battery-posts  assembled  in 
such  manner  that  everything  is  bolted  tightly  and  securely  together, 
and  kept  so,  and  the  jar  and  vibration  reduced  to  a  minimum,  the 


28 


CONCRETE   MORTAR-BLOCK 


breakage  of  parts  is  less  than  with  the  wood  block.  The  experience 
with  concrete  blocks  has  dispelled  the  former  erroneous  belief  that 
battery  parts  required  to  be  cushioned,  and  has  indicated  that  all 
parts  should  be  as  rigid,  as  solid,  and  as  inelastic  as  a  line-shaft 
in  its  bearings.  The  concrete  block  costs  less  to  build  under  aver- 
age conditions  than  the  wood  block.  It  gives  a  cleaner  looking  mill, 
and  does  not  decay.  By  its  solidity  and  non-cushioning  effect,  it 


CONCRETE    MORTAB-BLOCK    WITH    POCKETS    FOR    ANCHOR    BOLTS    AND    CAST-IRON    BED- 
PLATES  FOB   SECURING   BATTERY   POSTS. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 

increases  the  capacity  of  a  stamp  as  much  as  33%%  over  the  wooden 
block,  and  herein  is  the  reason  for  using  concrete  blocks. 

It  must  be  admitted  that  concrete  blocks  have  been  unsatisfactory 
in  a  number  of  cases,  while  the  wooden  block  has  given  satisfaction 
in  practically  every  instance.  This  has  been  due  to  defective  con- 
struction or  failure  to  appreciate  the  nature  of  block  required.  A 
high  narrow  pedestal  having  the  same  dimensions  and  small  base 
area  as  the  wooden  block  is  liable  to  crack  and  crumble  under  the 
tremendous  strain  and  vibration  from  the  constantly  recurring 


DEFECTS   IN    CONCRETE   MORTAR-BLOCK 


29 


blows  of  heavy  stamps.  What  is  required  is  a  block  of  broad  area 
receiving  the  strain  and  shock  from  a  broad  mortar  base  and  trans- 
mitting it  into  the  earth  with  as  small  a  strain  per  square  inch  of 
horizontal  area  as  possible. 


R 


The  principal  troubles  with  concrete  blocks  have  been:  A  rock- 
ing of  the  block,  due  to  imperfect  setting  on  bedrock  or  to  too  small 
a  base  area  when  set  on  loose  ground.  A  disintegration  of  the  block 


30  CONSTRUCTION   OF    CONCRETE   BLOCK 

due  to  not  tamping  the  concrete  sufficiently  during  construction,  to 
the  use  of  poor  material,  or  to  the  use  of  too  small  a  base  area  and 
too  narrow  a  block.  A  crumbling  of  the  top-dressing  or  grouting, 
improperly  put  on  for  the  purpose  of  leveling  it  after  the  block 
had  partly  set. 

An  instance  may  be  given  as  a  good  illustration  of  concrete 
mortar-block  troubles.  After  the  blocks  had  partly  set,  they  were 
grouted  up  one  inch.  A  short  time  after  the  mill  began  operating, 
the  grouting  began  to  crumble,  resulting  in  the  battery-posts  danc- 
ing and  the  mortars  shifting.  Then,  within  a  short  time,  occurred 
breaking  of  parts,  such  as  driving-pulley  plates,  cam-shafts,  cams, 
stems,  and  mortar  anchor  bolts. 

Grouting  the  blocks  has  been  successful,  but  in  view  of  the  large 


EBECTING  STAMP-BATTERY   FOUNDATIONS  AT  GOLDKIKLD   CONSOLIDATED   MILL. 

(Allis-Chalmers  Co.,  Milwaukee,  Wis.) 

number  of  cases  in  which  it  has  not,  it  is  inadvisable  to  take  such 
chances.  It  is  necessary  to  make  the  surface  of  the  block  absolutely 
true,  though  it  may  vary  a  small  fraction  of  an  inch  from  being 
level;  this  can  be  accomplished  by  chiseling  and  scraping  the  block 
after  it  has  partly  set,  or  by  promptly  bolting  a  wooden  frame  to 
the  top  of  the  block  by  means  of  the  anchor  bolts,  to  press  it  into 
shape,  before  it  has  had  time  to  set. 

Anchor  bolts  are  set  solidly  in  the  concrete,  or  are  placed  in  pipes 
embedded  in  the  concrete  or  in  recesses  so  that  they  may  be  readily 
replaced  if  sheared  and  broken.  The  shearing  and  breaking  of 
anchor  bolts  seems  to  be  due  to  the  bolts  being  too  small  in  diameter 
and  too  few  in  number,  and  more  so  to  a  neglect  to  keep  the  mortar 


BOLTING    MORTAR   TO    BLOCK  31 

securely  bolted  down.  When  bolts  embedded  in  concrete  are  broken 
they  cannot  be  repaired  or  replaced,  except  by  blasting  the  block 
to  pieces  and  rebuilding  it.  It  is  considered  that  by  using  eight 
bolts  of  good  material  and  2l/2  in.  diameter  to  each  mortar  and  by 
keeping  the  mortar  bolted  tightly  down,  no  trouble  will  be  exper- 
ienced unless  the  top  of  the  block  crumbles  so  that  the  mortar  does 
not  rest  firmly  and  securely.  Half  this  number  of  bolts  is  ordinarily 
sufficient.  This  is  the  rational  method  of  building  the  blocks,  but 
at  present  the  designs  allowing  the  bolts  to  be  easily  renewed  are 
preferred,  and  will  continue  to  be  preferred  until  it  is  fully 
demonstrated  that  concrete  blocks  can  be  built  with  solid  anchor 


SeCT/ONOf-  BffTTFKY  FOUNDATION. 
MORTAR-BLOCK   AT   GOLDFIELD   CONSOLIDATED    MILL. 

bolts  that  will  not  break.  The  objection  to  the  designs  allowing 
the  bolts  to  be  removed  are  that  there  is  a  reduction  of  the  large 
horizontal  cross-section  so  desirable  in  a  block,  and  that  the  blocks 
are  more  difficult  to  build. 

Iron  anvil-blocks  between  the  mortar  and  the  concrete  are  super- 
fluous and  seldom  used,  except  beneath  mortars  having  narrow  bases 
and  intended  for  wooden  blocks,  the  mortars  for  concrete  blocks 
having  bases  especially  wide  and  thick.  A  sheet  of  %-in.  rubber  is 
placed  between  the  mortar  and  the  block,  not  with  the  idea  of 
cushioning  the  force  of  the  stamp  blows,  but  to  make  an  even  bear- 
ing which  will  equalize  any  slight  irregularities  of  the  concrete 


32 


BOLTING   BATTERY-POSTS   TO    MORTAR-BLOCK 


surface  and  one  into  which  water  cannot  enter,  for  a  combination 
of  moisture  and  a  slight  jar  or  working  of  the  mortar  would  tend 
to  disintegrate  the  block.  Likewise,  a  sheet  of  rubber  should  be 
placed  between  the  concrete  block  and  the  iron  bed-plates  into  which 
the  bottoms  of  the  battery-posts  are  bolted,  or  the  bed-plates  will 
wear  down  into  the  concrete  under  jar. 


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f 



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rf^i  r  ' 

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k         Jf 

'--fos, 

tXJ 

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u 


STANDARD     TYPE    OF    BATTERY-POST 
SHOE. 


EXTRA    HEAVY    TYPE    OF    BATTERY- 
POST    SHOE. 


(Denver  Engineering  Works  Co.,  Denver,  Colo.) 

There  has  been  a  question  with  builders  as  to  whether  the  battery- 
posts  should  rest  in  cast-iron  foot  or  bed-plates  bolted  to  the  con- 
crete, or  in  wooden  sills  bolted  to  the  concrete  as  with  wooden 
blocks.  With  the  posts  resting  on  timbers,  these  timbers  will  absorb 
and  minimize  the  jar  and  vibration  to  some  extent,  thus  relieving 
the  battery-posts  and  lessening  the  pounding  between  the  cam-shaft 
and  its  boxes;  but  given  good,  wide  surfaces  in  both  the  block  and 
the  mortar,  with  the  mortar  and  battery-posts  bolted  securely  to 
the  block,  there  will  be  a  minimum  of  jar  and  vibration,  and  to  just 
the  extent  that  this  is  reduced  will  the  breakages  and  wear  and  tear 
be  reduced.  The  bolting  of  the  battery-posts  into  wide,  heavy  bed- 
plates securely  anchored  to  the  concrete  is  much  to  be  favored. 

Mortar-blocks  for  small  mills  are  usually  of  wood,  consisting  of 
pitch  pine  of  such  size  that  two  pieces  bolted  together  make  a 
block,  down  through  various  sizes  to  ordinary  planking  spiked  into 
a  solid  block  of  the  desired  dimensions.  They  should  be  coated 
with  a  preservative  paint  to  lessen  the  tendency  to  rot.  In  length 
they  vary  from  8  to  25  ft.  Where  solid  rock  cannot  be  secured,  a 
bed  of  concrete  2  or  3  ft.  thick  and  as  wide  as  4  ft.,  is  made  as  a 
foundation.  Even  where  bedrock  is  found,  a  bed  of  concrete  1  ft. 
thick  is  advisable  to  give  a  level  surface  for  the  block  to  rest  on, 


WOOD   MORTAR-BLOCK  33, 

and  to  fill  crevices  or  weak  spots  in  the  rock.  After  the  block  is 
set  in  place,  sand  is  filled  around  it  and  tamped  down.  Pouring  in 
concrete  has  been  tried,  but  is  not  recommended  on  account  of  its 
shrinking.  The  nuts  of  the  anchor  bolts,  tie  rods,  and  all  others 
about  the  battery  should  be  frequently  tightened  after  the  mill  goes 
into  operation. 


CHAPTER  II 

MORTAR  AND  MORTAR  LINER — SHOE  AND  DIE — BOSSIIEAD — TAPPET — 

CAM. 

Mortar  and  Mortar  Liner. — The  mortar  is  made  of  cast  iron,  and 
is  approximately  six  or  more  times  heavier  than  the  weight  of  the 
stamp  to  be  used  in  it.  The  mortar  has  been  made  heavier  since 
the  introduction  of  concrete  mortar-blocks,  not  alone  in  accordance 
with  the  increased  weight  of  stamps,  but  also  heavier  in  proportion 
to  the  other  parts ;  the  trend  now  being  in  the  direction  of  a  wide 
and  extra  thick  base.  This  is  to  secure  exceptional  rigidity  and 
strength  for  the  same  reasons  that  concrete  mortar-blocks  are  made 
massive  and  heavy. 

In  selecting  a  mortar  for  rapid  crushing,  it  is  advisable  to 
get  a  narrow  one,  the  best  known  type  being  the  'Homestake.' 
All  manufacturers  make  a  mortar  of  this  kind.  By  a  narrow, 
rapid-crushing  mortar  is  meant  one  having  as  little  spare  room 
in  its  crushing  area  as  possible.  Such  a  mortar  is  usually  about 
12  in.  wide  at  the  discharge-lip,  and  there  is  no  surplus  space  at 
the  ends.  The  inside  back  of  many  of  these  mortars  is  vertical,  or 
practically  so,  which  has  given  rise  to  the  term  'straight-back' 
mortars.  It  may  be  urged  that  but  little  inside  amalgamation  can  be 
done  with  such  a  mortar.  This  idea  is  erroneous,  for  inside  amalga- 
mation ordinarily  increases  with  the  height  of  the  discharge,  which 
is  the  vertical  distance  between  the  tops  of  the  dies  and  the  bottom 
of  the  screen.  A  chuck-block  plate — the  term  applied  to  the  front 
inside-amalgamating  plate — and  in  some  cases  a  back-plate,  can  be 
used  in  these  mortars,  though  it  will  require  some  care  and  extra 
trouble.  Inside  amalgamation,  as  referring  to  the  catching  of  a  large 
part  of  the  gold  inside  the  mortar,  is  going  out  of  use.  Capacity 
is  being  called  for,  and  the  tendency  toward  outside  amalgamation, 
or  at  least  toward  not  requiring  so  large  a  proportion  of  the  gold  to 
be  caught  inside  the  mortar  at  the  expense  of  capacity,  is  increas- 
ing. It  has  been  suggested  that  by  using  a  wide  mortar  it  may  be 
lined  and  thus  converted  into  a  narrow  one  if  desired.  It  is  hard, 
however,  to  get  special  liners  made  that  will  not  give  trouble  by 
coming  loose.  It  would  be  almost  impossible  to  decrease  the  horizon- 
tal distance  between  the  die  and  the  screen.  However,  the  idea  has 
some  merit  and  can  be  applied  to  wide  mortars  now  in  use.  The 

34 


35 


RAPID    CRUSHING    MORTAR    OF    HOMESTAKE    TYPE. 

A — Liners.  B — Die.  C— False  die.  D — Chuck-block.  E — Screen  frame. 
F — Closing  board.  G — Splash-board.  H — Extension  mortar  lip  or  distribut- 
ing box.  I — Lug  and  key  holding  chuck-block.  J — Key  holding  screen  frame. 
K — Shoe.  L — Bosshead.  M — Stem.  N — Cover  boards.  0 — Copper  chuck- 
block  plate.  P— Copper  splash-plate.  Q — Copper  lip-plate.  R — Screen. 


36 


TYPES   OF    MORTARS 


feed-mouths  of  mortars  should  be  wide,  so  that  coarse  rock  may  be 
fed  to  them  during  break -downs  of  the  rock-crusher. 

The  'open-front'  mortar  is  one  of  the  newer  designs  to  enable 
easy  handling  of  the  long  and  heavy  bossheads  of  heavy  stamps. 
The  front  part  of  the  mortar  above  the  screen-opening  is  not  cast 


STRAIGHT-BACK  RAPID-CRUSHING  MOBTAR  WITH  NARROW  BASE  FOR  WOOD  MORTAR- 
BLOCKS.  FITTED  WITH  LINERS,  CHUCK-BLOCK,  AND  DISTRIBUTING  BOX  BOLTED 
TO  MORTAR  LIP. 

(Union  Iron  Works  Co.,  San  Francisco.) 

solid,  but  is  a  separate  piece  which  is  bolted  in  place  and  is  easily 
removed. 

Double-discharge  mortars,  with  a  screen  opening  in  front  and 
behind,  have  been  tried,  but  are  not  considered  successful.  The 
back-screen  is  hard  to  get  at,  and  to  hold  in  place  without  coming 
loose.  There  appears  to  be  so  much  motion  to  the  pulp  that  it  does 
not  settle  on  the  dies,  and  in  consequence  the  mortars  frequently 


WEAR   ON    MORTAR 


37 


fill  up  with  ore  and  pulp,  especially  when  feeding  fine  material.  So 
much  water  is  required  to  get  a  proper  action  of  the  pulp  along  the 
screen  that  the  outside  plates  cannot  do  good  amalgamating  with  the 
dilute  pulp  that  results.  The  single-discharge  mortar  can  be  made 
to  discharge  the  pulp  about  as  fast  as  made  when  treating  ordinary 
rock.  Iii  view  of  this  and  of  the  inconvenience  in  working  with  a 


NARROW    MORTAR   SPECIALLY   DESIGNED   FOE  THE   USE   OF  A   BACK   AMALGAMATING 
PLATE  AS   WELL  AS   A  CHUCK-BLOCK   PLATE. 

(Chalmers  &  Williams,  Chicago  Heights,  111.) 


double-discharge,  these  mortars  are  usually  found  with  the  backs 
closed,  except  with  such  easily  disintegrated  material  as  gravel, 
where  the  problem  becomes  one  of  screening  rather  than  crushing. 

Mortars  are  ruined  or  worn  out  in  two  ways,  by  being  cracked 
or  by  being  worn  through  by  the  attrition  of  the  pulp.     Cracking 


38  MORTAR   LINER 

is  due  to  imperfections  in  the  mortar  as  manufactured,  and  to  loose 
and  shifting  dies  without  a  cemented  layer  of  sand  underneath  to 
absorb  and  spread  the  shock  or  impact  of  the  stamp.  This  is  in 
connection  with  poor  feeding  whereby  the  stamp  shoe  strikes  the 
die  destructively,  instead  of  being  properly  cushioned  on  a  bed  of 
ore  and  pulp  over  the  die.  With  mortars  that  are  suitably  lined 
the  wear  through  the  attrition  of  the  pulp  is  small.  Mortars  that 
are  cracked  or  worn  through  are  patched  by  having  steel  or  iron 
plates  bolted  to  them. 


STANDARD   SIZE  FIVE-STAMP   MORTAR  IN   SECTIONS   OF   NOT  EXCEEDING   332   POUNDS 
FOR  EASY  TRANSPORTATION  BY   MULEBACK. 

(Colorado  Iron  Works  Co.,  Denver,  Colo.) 

Mortars  should  be  lined  in  the  front,  back,  ends,  bottom,  and 
where  the  feed  strikes  the  mortar  at  the  bottom  of  the  feed  slot. 
The  front,  back,  and  end-liner  should  dovetail ;  though  liners  having' 
bevel  ends,  so  as  to  lock  themselves  in  position  by  bevel  joints,  have 
given  satisfaction.  The  back-liner  may  or  may  not  be  finally  bolted 
into  place.  Attention  should  be  given  to  securing  liners  so  that 
they  will  not  come  loose.  A  bottom-liner  of  one  piece  is  usually  a 
nuisance ;  sand  and  pieces  of  iron  creep  under  the  ends,  causing 
the  liner  to  sag  in  the  middle,  when  a  general  movement  begins 
which  may  result  in  displacing  the  dies  when  they  become  worn 
down.  Two-piece  liners  act  in  a  similar  way.  Individual  plates  or 


SETTING   DIE    IN    MORTAR 


39 


'false  dies'  are  what  is  required.  Old  dies  worn  smooth  and  down 
to  a  thickness  of  twro  inches  answer  well.  An  inch  of  sand  should 
be  placed  between  them  and  the  mortar  below,  likewise  between 
them  and  the  'true  dies'  above.  This  has  been  condemned  on  the 
ground  that  it  cushions  and  consequently  lessens  the  efficiency  of 
the  stamp  blows,  but  its  use  will  reduce  the  chances  of  cracking 
the  mortar  or  the  dies.  The  dies  should  be  plumbed  exactly  under 
each  stamp,  and  should  fit  snugly  in  the  mortar,  with  just  enough 
space  intervening  that  they  may  be  pried  out  without  too  much 
trouble  from  locking  each  other.  Should  there  be  any  surplus  room 


Front  view. 

The  part  of  mortar  above  screen 
opening  can  be  removed  for  easy 
replacement  of  stems  and  bossheads. 


Back  view. 

Showing  water  connections  to  in- 
troduce battery  water  under  pres- 
sure to  the  face  of  each  die. 


OPEN-FRONT   MORTAR   WITH    STRONG  BASE   FOR  HEAVY    STAMPS. 

(Allis-Chalmers  Co.,  Milwaukee,  Wis.) 

at  the  ends  or  sides,  the  dies  should  be  wedged  with  a  piece  of  iron 
or  steel.  This  wedging  is  likely  not  to  hold  when  the  dies  become 
worn,  consequently  steps  should  be  taken  to  secure  liners  that  will 
completely  take  up  this  surplus  space,  thus  enabling  the  dies  to  hold 
themselves  securely  in  place.  There  is  nothing  more  annoying  than 
a  mortar  so  large  that  the  dies  shift  from  their  proper  position  under 
the  stamps.  In  putting  in  a  new  set  of  dies,  it  is  advised  to  pack 
coarse  rock  around  them  and  to  run  with  a  heavy  feed,  that  is, 
with  a  thick  bed  of  pulp  on  the  dies,  for  a  few  hours  until  the  dies 
have  been  solidly  cemented  in  place. 

A  shallow  mortar  should  be  ordered  if  it  is  expected  to  use  a  low 
discharge  in  crushing.  Use  a  high  chuck-block — a  long  piece  of 
wood  filling  the  front  of  the  mortar  at  the  bottom  of  the  screen- 


40  MATERIAL  FOR  SHOE  AND  DIE 

frame — when  starting  a  new  set  of  dies.  And  decrease  the  screen- 
height  an  inch  at  a  time,  as  the  dies  wear  down,  by  chuck-blocks  and 
wooden  strips  of  various  thicknesses,  until  at  the  last  lowering  of 
the  screen,  just  before  discarding  the  worn-out  dies,  there  is  nothing 
placed  underneath  the  screen-frame.  In  short,  keep  the  height  of 
discharge  as  nearly  constant  as  possible  by  lowering  the  screen  an 
inch  at  a  time,  as  the  dies  wear,  and,  if  possible,  do  not  move  the 
dies  until  worn  out.  It  may  be  necessary,  with  a  deep  mortar,  to 
build  up  the  old  or  partly  worn  dies  by  false  dies.  Where  the  dies 
are  removed  in  the  monthly  clean-up,  start  the  new  dies  without  the 
false  ones,  and  insert  the  false  dies  at  the  next  clean-up  after  these 
new  dies  have  been  worn  down. 

Shoe  and  Die. — The  shoe  and  die  are  made  of  iron  and  steel  of 
several  kinds,  going  under  such  names  as  cast  and  chilled  iron, 
hammered,  forged,  cast,  chilled,  chrome,  and  manganese  steel,  and 
semi-steel.  The  millman  will  decide  for  himself  when  choosing  from 
these,  keeping  in  mind  the  local  conditions  affecting  the  nature  of 
the  ore  and  the  cost  of  supplies.  It  is  usually  cheaper  to  use  steel 
than  iron,  despite  its  increased  cost,  on  account  of  the  smaller  con- 
sumption of  steel  per  ton  of  ore  crushed  and  the  less  time  lost  in 
renewals  and  setting  of  the  tappets.  For  the  latter  reason  steel 
shoes  and  dies  are  much  preferred  by  millmen.  The  life  of  a  set 
of  steel  shoes  and  dies  may  roughly  be  estimated  at  four  months 
or  less,  as  against  half  that  length  of  time  for  iron,  though  the  life 
of  steel  parts  has  shown  on  different  ores  such  wide  variations  as 
from  2%  to  9  months,  and  four  times  that  of  iron.  A  material  having 
the  maximum  hardness  and  the  minimum  brittleness  is  desired.  The 
limit  of  hardness  is  passed  when  the  shoes  and  dies  chip,  crack,  or 
break.  The  remedy  in  this  case,  presuming  that  the  feed  has  not 
been  kept  too  low  or  the  drop  too  long  for  the  nature  of  the  ore 
fed,  is  to  use  a  softer  die;  if  the  trouble  continues,  keep  trying  a 
softer  material  for  the  die  until  the  proper  limit  is  reached.  How- 
ever, it  should  be  remembered  that  a  shoe  or  die  of  steel  or  other 
material  of  one  maker  may  be  as  unsatisfactory  as  those  of  another 
maker  may  be  satisfactory, .  due  to  a  variation  in  composition  and 
method  of  manufacture.  It  may  be  that  the  shoe  in  use  is  too  hard 
and  brittle,  when  a  softer  one  or  another  kind  should  be  tried,  but 
not  one  as  soft  as  the  die.  The  wear  is  greater  on  the  shoe,  and  it 
should  have  the  harder  metal.  With  a  die  softer  than  the  shoe,  the 
two  wearing  faces  adjust  themselves  well  to  each  other.  The  varia- 
tion of  life  between  a  steel  and  iron  shoe  is  much  greater  than  be- 
tween a  steel  and  iron  die.  For  these  various  reasons  many  mills 


IRON   VS.    STEEL   FOR   SHOE   AND   DIE 


41 


are  found  using  steel  shoes  and  iron  dies  with  great  satisfaction. 
The  use  of  a  steel  shoe  with  a  semi-steel  die  is  recommended  as  the 
combination  that  will  probably  prove  the  most  satisfactory  in  the 
majority  of  cases,  though  the  softer  the  ore,  and  to  some  extent  the 
finer  the  ore,  the  softer  the  material  that  may  be  successfully  and 
economically  used  in  the  shoes  and  dies. 

With  steel  shoes  and  dies  the  amount  of  metal  used  or  consumed  in 


- 


STAMP   SHOE  AND   DIE. 

(Chrome  Steel  Works,  Chrome,  N.  J.) 


crushing  will  vary  from  one-half  to  one  pound  per  ton  of  ore  crush- 
ed, 60  to  66%%  of  which  will  be  from  the  shoe.  Under  exceptional 
conditions  the  amount  may  be  greater  or  less  than  this  approxima- 
tion. With  iron  shoes  and  dies  the  consumption  may  reach  double 
this  amount.  With  steel  shoes  and  iron  dies  the  consumption  of 
each  will  tend  toward  being  equal.  As  the  ore  fed  to  the  mortar 
becomes  coarser  or  harder,  and  the  bed  of  ore  over  the  die  becomes 
thinner  than  normal  or  the  feeding  is  poorly  done,  the  consumption 
of  metal  increases.  As  the  ore  is  crushed  and  discharged  coarser 
from  the  mortar  and  the  tonnage  thus  increased,  and  generally  as 


42  IRREGULAR   WEAR   OF   DIE 

the  tonnage  is  increased  in  any  manner,  the  consumption  of  metal 
per  ton  of  ore  crushed  becomes  correspondingly  less,  for  the  life  of 
the  parts  in  days  of  wear  will  not  vary  greatly. 

Should  the  die  be  found  to  wear  unevenly  on  one  side,  it  may  be 
due  to  a  soft  spot  in  the  metal,  which,  once  started,  increases,  or  it 
may  be  due  to  some  inexplicable  trouble  in  the  feeding  of  the  mortar. 
The  die  should  be  turned  half-way  around  in  the  effort  to  make  it 
wear  evenly.  At  some  mills  the  dies  removed  when  cleaning  up  the 
mortars  are  returned  to  the  same  exact  place  and  position,  at 
others  they  are  turned  half-way  around,  and  in  other  mills  no  at- 
tempt is  made  to  return  them  to  any  particular  position.  If,  on 
examination  before  removing,  the  dies  appear  to  be  wearing  evenly, 
and  do  not  exhibit  a  tendency  to  wear  unevenly  in  some  general 
direction,  it  is  unnecessary  to  use  care  to  return  them  to  any  particu- 
lar position,  as  a  shoe  and  die  soon  adjust  themselves  to  each  other. 
When  dies  wear  unevenly  on  one  edge,  the  greater  wear  is  usually 
on  the  side  toward  the  back  of  the  mortar,  and  consequently  it 
should  be  made  a  rule  in  returning  dies  to  the  mortar  in  ordinary 
cases,  to  place  the  less  worn  edge  or  higher  side  to  the  back  of  the 
mortar. 

The  shoe  generally  wears  to  an  even,  slightly  concave  face,  while 
the  die  wears  convex  in  a  corresponding  manner,  this  is  called 
'cupping;'  the  parts  are  said  to  'cup.'  The  evenness  of  this  cup- 
ping is  due  to  the  rotation  of  the  stamps  in  falling,  to  the  dies  being 
plumbed  exactly  underneath  the  shoes,  and  to  closely  fitting  guides 
which  enable  the  shoe  to  strike  the  die  exactly  central  at  each  drop. 
No  die  should  be  permitted  to  stand  higher  or  lower  than  the 
others  or  it  will  cause  that  stamp  to  'pound'  or  to  'cushion'  through 
having  too  thin  or  too  thick  a  bed  of  pulp  over  its  corresponding 
die.  In  the  effort  to  economize  by  saving  'steel' — the  general  term 
for  shoes  and  dies, — the  die  is  usually  worn  to  a  thickness  of  1  or 
iy2  in. ;  at  less  than  this  thickness  it  is  liable  to  break  at  any  time. 
When  a  die  breaks  in  a  set  that  is  only  partly  worn  out,  another 
of  the  same  height  must  be  put  in  its  place.  If  no  die  of  this  height 
is  available,  a  new  set  should  be  put  in,  though  it  is  possible  to  re- 
place the  broken  die  with  a  shorter  one  built  up  by  a  false  or  old 
die.  All  mills  have  on  hand  an  assortment  of  partly  worn  shoes 
and  dies  of  various  heights  for  this  purpose,  or  for  replacing  a  die 
that  should  be  removed  from  a  set  because  of  some  abnormality  in 
its  wear.  Worn-out  dies  and  discarded  mortar  liners  and  plates  of  jaw- 
crushers  can  be  used  in  lining  ore-chutes.  The  die  should  be  of  ex- 
actly the  same  diameter  as  the  shoe  or  ^4  in-  larger,  as  the  shoe, 


FASTENING   SHOE   TO   BOSSHEAD  43 

through  the  looseness  of  the  guides,  strikes  over  an  area  slightly 
greater  than  its  face. 

For  securing  shoes  in  the  bosshead,  hardwood  wedges  made  from 
staves  of  nail  kegs  or  barrels  are  tied  around  the  shanks  of  the 
shoes.  Soft  wood  can  be  used  if  it  is  of  a  tough,  pliable  nature,  but 
the  shoes  come  off  so  easily  that  its  use  is  not  advised.  Thick 
wedges  can  be  used  where  the  space  calls  for  thin  ones,  by  spacing 
them  some  distance  apart  about  the  shank,  and  allowing  them  to  be 
crushed  into  shape  when  the  shoe  is  put  on.  With  the  old  style  of 
iron  bosses,  having  a  ring  on  the  lower  end,  the  shoulder  of  the 
shoe  should  not  come  in  contact  with  the  boss  or  it  will  tend  to 
loosen"  the  ring.  In  bosses  without  these  rings,  the  shoe  may  be 
wedged  so  that  it  will  be  driven  up  flush  with  the  boss,  for  the 
shoe  can  then  be  worn  to  almost  the  thinness  of  cardboard  before 
breaking.  However,  there  is  then  no  room  for  the  shoe  to  be 
driven  further  into  the  socket  and  thus  wedged  tighter  if  the  shoe 
should  tend  to  come  loose.  Therefore  many  millmen  aim  to  wedge 
the  shoe  so  that  one-third  inch  will  intervene  between  its  shoulder 
and  that  of  the  bosshead. 

For  removing  the  worn-out  shoes,  a  'drift'  of  tough  steel  is  in- 
serted in  the  key-way  in  the  centre  of  the  bosshead  and  pounded 
in,  the  wedging  tension  causing  the  shoe-shank  to  be  forced  out 
of  the  socket.  Where  the  shank  does  not  extend  into  the  field  of 
the  key-way,  a  'dutchman, '  that  is,  a  piece  of  metal  2  in.  long, 
usually  a  broken  tappet-key,  is  slipped  in  on  top  of  the  shank, 
and  the  'drift'  is  carefully  inserted  to  make  a  tight  fit  before  driv- 
ing. The  edges  of  the  'drift'  should  be  greased  to  make  it  drive 
easier.  Shoes  are  also  removed  by  blowing  them  out  with  small 
charges  of  dynamite.  Should  the  ring  of  wooden  wedges  remain 
'frozen'  to  the  socket  without  dropping  out  with  the  shank,  it 
should  be  allowed  to  remain,  and  in  putting  on  a  new  shoe,  a 
square  piece  of  canvas  is  laid  on  the  shank  or  a  few  new  thin 
wedges  tied  about  it. 

In  putting  on  a  new  set  of  shoes,  the  stems  are  first  cleaned  of 
the  grease  below  the  tappets  by  passing  a  long  strip  of  burlap  or 
cloth  wet  with  kerosene  or  gasoline  about  the  stem  and  alternately 
pulling  each  end  of  the  cloth  until  the  stem  is  clean.  This  is  neces- 
sary as  the  tappet  will  now  be  set  in  the  cleaned  part — it  would 
be  impossible  to  make  two  slippery,  greasy  metal  surfaces  hold 
together.  The  tappet-keys  are  loosened  and  the  stem  pulled  up 
through  the  tappet  by  means  of  the  overhead  chain-blocks  until 
the  boss  is  raised  sufficiently  to  allow  a  new  shoe  to  be  set  under- 


44  PUTTING   ON   A   SET   OF   SHOES 

neath,  when  the  tappet  keys  are  driven  in  sufficiently  tight  for 
security,  and  the  chain-blocks  removed.  The  new  shoes  are  now 
rolled  on  a  plank  up  to  the  mouth  of  the  mortar;  they  are  stood  on 
the  mortar  lip  and  the  wooden  wedges  tied  about  the  shanks ;  then 
they  are  slipped  in  upon  the  dies  underneath  the  bosses.  The  stem 
is  now  dropped,  using  a  thick  cam-stick  to  increase  the  height  of 
drop.  As  the  stem  drops,  the  millman  places  his  hand  on  the  tap- 
pet that  he  may  be  able  to  tell  by  the  jar  if  the  shoe  has  been  picked 
up  by  the  boss.  He  keeps  the  cam-stick  between  the  tappet  and 
the  cam  at  each  lift  of  the  stamp,  so  as  to  give  the  stamp  a  higher 
drop,  and  consequently  a  greater  driving  effect.  It  also  causes 
the  stamp  to  revolve  more,  insuring  a  straighter  driving  *of  the 
shoe-shank  into  the  boss.  As  the  shoe  is  lifted  the  first  time,  the 
man  at  the  mortar  below  throws  underneath  it  a  shovelful  of  fine 
rock  or  pulp  to  cushion  the  blow  and  prevent  cracking  or  chip- 
ping of  the  shoe  or  die.  The  operation  is  spoken  of  as  'driving 
on  shoes,'  and  is  followed  by  setting  each  stamp  to  drop  the  exact 
height  desired.  Some  millmen,  instead  of  driving  the  tappet-keys 
in  lightly  the  first  time,  set  the  tappets  permanently  and  do  not 
re-set  them  after  the  shoes  are  on.  This  results  in  the  height  of 
drop  being  a  little  irregular,  but  some  men  are  able  to  calculate 
so  closely  just  how  far  the  shoe  will  be  driven  into  the  boss  that 
the  plan  is  often  a  good  one.  When  tying  wedges  around  a  shoe 
resting  under  a  boss,  it  should  be  made  a  habit  to  pull  the  shoe 
out  sufficiently,  so  that,  should  the  stamp  accidentally  or  otherwise 
drop  off  the  finger- jack — the  prop  upon  which  the  tappet  is  sup- 
ported when  the  stamp  is  'hung  up' — it  will  fall  on  top  of  the 
shank  instead  of  encircling  it,  as  many  men  have  had  fingers  cut 
off  in  this  way.  A  safer  and  more  expeditious  method  is  to  tack 
the  wooden  wedges  to  a  strip  of  drilling,  making  a  ring  that  can 
be  quickly  slipped  over  the  shank  of  the  shoe  before  placing  the 
shoe  beneath  the  boss.  A  useful  aid  to  putting  on  the  wedges  is 
to  make  five  or  ten  smooth  cylinders  of  wood,  each  having  a  diam- 
eter equal  to  the  average  diameter  of  the  shoe-shank  and  a  slightly 
tapered  length  equal  to  the  height  of  the  wedges.  The  wedges  are 
tied  about  these  cylinders  so  that  when  a  shoe  is  to  be  put  on,  it 
is  only  necessary  to  set  the  cylinder  on  top  of  the  shoe-shank  and 
slip  the  circlet  of  wedges  down  over  the  shank.  Care  should  be 
exercised  that  the  mortar  is  not  overfed  for  some  time  after  shoes 
are  put  on,  since  running  mortars  choked  tends  to  cause  the  shoes 
to  come  off. 

Should  a  shoe  come  off,  and  the  boss  continue  to  drop  encircling 


IRON   VS.    STEEL   FOR   BOSSHEAD 


45 


the  shank,  the  socket  of  the  boss  will  soon  be  worn  so  large  that 
a  shoe  cannot  again  be  fastened  in  it.  Should  the  shoe  turn  partly 
or  completely  over  on  its  side,  the  shoulder  of  the  boss  may  be 
so  battered  that  it  may  be  considered  necessary  to  remove  it  and 
chip  out  the  socket.  Instead  of  doing  this,  the  boss  should  be  set 
to  drop  encircling  the  shoe-shank  with  a  height  of  2  or  3  in.,  after 


BOSSHEAD.  THREE-KEY    TAPPET. 

(Chrome  Steel  Works,  Chrome,  N.  J.) 

which  the  entire  battery  should  be  run  for  a  half-hour,  when  the 
socket  should  be  worn  to  its  normal  size. 

Bosshead. — The  bosshead,  or  'boss'  for  short,  was  formerly  made 
of  iron,  but  now  of  cast  steel,  as  steel  is  less  liable  to  be  split  by 
the  wedging  tendency  of  the  tapered  stem  or  shoe-shank,  or  by  the 


46 


TAPPET    COUNTER-BORES 


blowing  out  of  shanks  or  broken  stem-ends  with  dynamite.  An 
additional  reason  is  that  there  is  much  wear  on  the  lower  part  of 
the  boss  by  the  attrition  of  the  pulp  when  the  shoes  are  well  worn 
down,  as  can  be  seen  by  examining  the  bosses  that  have  been  in 
use  for  a  long  time.  Steel  is  better  able  to  resist  this  abrasion, 
as  is  shown  by  the  comparative  life  of  iron  and  steel  shoes  and  dies. 
Tappet. — The  tappet  should  be  of  cast  steel,  being  more  durable 
than  cast  iron.  It  is  counter-bored  at  each  end  to  have  a  recess 
of  y±  to  %  in.  wide  and  l/2  in.  or  more  deep,  so  that  the  entire  face 
of  the  tappet  exposed  may  come  in  contact  with  the  cam  which 
it  rides,  and  thus  wear  evenly.  As  the  cam  must  be  placed  a  frac- 
tion of  an  inch  away  from  the  stem,  if  the  tappet  were  not  counter- 


A 

1 

c 

4-i 

\ 

1 

"h 

'UJ 


.A — Stamp  Stem.    B — End  counterbores.    C — Keyway.    D — Gib.    E — Longi- 
tudinal counterbore. 


bored  in  this  way  a  thin  collar  of  metal  would  gradually  form  about 
the  stem  as  the  tappet-face  wore  down.  This  collar  would  inter- 
fere with  the  action  of  the  cam  on  the  tappet. 

The  tappet  should  have  a  slight  counter-bore  throughout  the 
main  bore  through  which  the  stem  passes,  and  on  the  side  opposite 
the  gib  or  small  piece  of  steel  enclosed  in  the  tappet  which  is 
wedged  against  the  stem,  by  driving  in  the  tappet-keys.  This 
counter-bore  should  be  of  a  smaller  radius  than  the  main  bore  of 
the  tappet,  and  should  make  the  main  bore  elliptical  in  form  by 
reaming  out  one-third  of  its  circumference.  When  the  tappet  is 
secured  to  the  stem  by  driving  the  keys  against  the  gib,  it  forces 
the  stem  into  the  elliptical  part  of  the  bore  and  gives  three. bearing 


TAPPET    GIB   AND    KEY  47 

surfaces  equidistant,  two  where  the  counter-bore  intersects  the  main 
bore,  and  one  at  the  gib,  whereas  there  are  only  two  in  a  tappet 
not  counterbored — one  at  the  gib  and  one  diametrically  opposite. 
The  use  of  three  bearing  surfaces  instead  of  two,  with  the  increased 
wedging  effect,  enables  the  tappet  to  be  firmly  fastened  without 
driving  the  keys  excessively  tight.  Slipping  of  tappets  is  one  of 
the  banes  of  a  niillmaii's  existence,  and  advantage  should  be  taken 
of  every  aid  to  prevent  it.  All  manufacturers  do  not  counter-bore 
the  tappets  in  this  manner,  and  this  point  should  always  be  taken 
up  when  purchasing  a  mill  or  ordering  new  tappets. 

Gibs  that  are  too  soft  tend  to  cut  out  at  the  key-ways  by  the 
frequent  driving  of  the  keys.  Placing  a  thick  metal  shim  between 
gibs  and  keys  will  prevent  this,  though  it  is  much  more  difficult 
to  keep  tappets  from  slipping  when  shims  are  placed  between  the 
gib  and  the  keys  than  when  placed  between  the  keys  and  the  out- 
side of  the  tappet  as  is  usually  done.  The  use  of  a  softer  metal 
in  the  key,  such  as  soft  steel  or  iron,  will  lessen  the  cutting  tend- 
ency. Gibs  that  are  cut  badly  should  be  removed,  that  is,  when 
they  are  cut  so  badly  that  the  tappet  keys  bind  on  the  tappet  in- 
stead of  against  the  gib.  Broken  gibs  should  also  be  replaced  or 
they  will  mar  and  scratch  the  stems.  Tappet-keys  are  re-shaped 
and  re-pointed  at  the  blacksmith-shop,  or  by  means  of  a  coarse 
file.  An  emery  wheel  is  an  excellent  tool  for  this  purpose  and  for 
grinding  amalgam  chisels,  as  well  as  for  a  multitude  of  other  uses 
about  a  mill  and  mine,  and  should  be  included  in  the  equipment 
of  every  mill.  For  driving  tappet-keys,  single-hand  hammers  with 
handles  a  little  longer  than  usual,  so  that  they  may  be  used  when 
necessary  with  two  hands  also,  should  be  employed.  When  tappet- 
keys  have  to  be  sledged  with  heavy  double-hand  hammers  to  pre- 
vent the  tappet  from  slipping,  something  is  wrong ;  usually  the  gibs 
are  cut  out  at  the  key-ways  and  the  tappets  are  bored  so  large 
in  comparison  to  the  diameter  of  the  stem  that  there  is  little 
binding  surface.  Where  the  slipping  is  thought  to  be  due  to  grease, 
the  tappet-keys  may  be  loosened  and  a  small  quantity  of  gasoline 
poured  into  the  upper  counter-bore  of  the  tappet  to  run  down 
between  the  tappet  and  the  stem,  and  thus  wash  out  the  grease. 
The  tappet  or  stem  has  sometimes  been  raised  and  the  binding 
surface  of  the  stem  wiped  clean  and  chalked,  with  the  idea  that 
the  chalk  by  its  fine  grit  might  increase  the  binding  effect ;  pow- 
dered resin  or  dust  has  been  introduced  between  the  tappet  and 
the  stem  for  the  same  purpose.  Gibs  with  their  curves  bored  to  a 
radius  slightly  smaller  than  that  of  the  stem  exert  a  good  clamp- 


48  TAPPET    GIB   AND   KEY 

ing  effect.  Dividing  the  gib  into  sections  enables  each  tappet-key 
to  clamp  its  own  gib  tight  to  the  best  advantage,  and  is  of  value 
with  an  extra  long  tappet. 

Tappets  should  be  bored  1/32  in.  larger  in  diameter  than  the  stems. 
It  should  be  possible  to  move  and  slide  them  easily,  but  no  loose- 
ness should  be  apparent.  Tappets  with  a  bore  of  Y64  in.  larger 
than  the  stem  have  been  used,  but  too  much  trouble  is  experienced 
in  slipping  them  over  irregularities  in  the  stem.  The  driving  of 
the  keys  should  be  done  evenly.  If  the  upper  or  lower  key  be 
driven  tight  before  starting  the  other,  it  may,  in  the  case  of  tap- 
pets bored  too  large,  throw  the  tappet  out  of  line  with  reference 
to  the  stem.  This  may  be  one  of  the  causes  of  stamps  twirling.  It 
may  also  serve  to  explain  the  lengthening  of  the  drop  of  a  stamp 
by  a  slipping  tappet,  which,  however,  is  rarely  seen ;  for  ordinarily, 
when  a  tappet  slips,  it  is  driven  upward  on  the  stem  by  the  re- 
peated blows  of  the  cam,  thus  lowering  the  stamp  until  the  shoe 
touches  the  die,  after  which  there  can  be  no  further  lifting  of  the 
stamp.  Taking  the  case  where  the  upper  key,  or  the  upper  part 
of  a  broken  gib,  is  driven  tight  first  and  the  tappet  is  slipping, 
the  gib  will  be  out  of  alignment  with  the  stem  and  the  upper  part 
of  the  gib  will  be  pressed  tightly  against  the  stem  while  the  lower 
part  is  inclined  from  it.  It  is  impossible  for  the  tappet  to  be 
driven  upward  as  usual,  for  the  upper  shoulder  of  the  gib  buries 
itself  in  the  stem  and  prevents  such  movement,  but  the  jar  and 
rebound  from  the  stamp  striking  the  die  causes  the  tappet  to  slip 
down  on  the  stem  a  little,  where  it  takes  a  new  grip  the  moment 
the  cam  strikes  it,  causing  it  to  drop  down  a  little  farther  when 
the  stamp  strikes  again.  This  continues  until  the  stamp  begins 
to  'cam,'  that  is,  to  fall  on  the  cam  from  having  too  long  a  drop 
for  the  speed  of  revolution. 

If  the  tappet-keys  on  each  battery  are  all  driven  in  on  the  same 
side,  that  is,  all  driven  in  either  on  the  right  or  the  left  side  of 
their  respective  stems,  there  will  be  less  trouble  from  the  locking 
or  meshing  of  keys  that  project  out  too  far,  or  are  slipping  out 
of  the  key-ways.  Tappets  are  often  made  with  the  key-ways  wider 
on  one  side  than  on  the  other,  so  that  the  keys  shall  be  driven  in 
from  the  wide  side.  This  is  imperative  only  when  the  gibs  are 
badly  worn,  but  in  such  cases  the  tappet  should  be  marked  by 
chalk  or  paint  to  denote  this  side,  unless  the  manufacturers  have 
marked  it. 

For  setting  the  tappets,  a  special  quick-acting  clamp  is  placed 
around  the  stem  at  the  required  distance  above  the  tappet,  which 


SETTING   THE   TAPPET 


49 


is  then  resting  on  the  finger-jack,  and  on  loosening  the  keys  the 
stem  drops  down  this  distance ;  the  clamp  is  then  removed  after 
tightening  the  keys.  Otherwise  the  chain-blocks  are  attached  to 
the  stem  to  raise,  lower,  or  hold  it.  In  setting  the  tappets,  a  man 
stands  on  each  of  the  two  opposite  sides;  one  places  a  'drift'  having 
an  eye  and  a  wooden  handle  against  the  end  of  the  key  and  loosens 
it  with  a  hammer,  but  does  not  drive  it  out,  while  the  man  on 
the  other  side  holds  the  tappet  steady,  and,  with  a  piece  of  cloth 
to  deaden  the  force  of  the  blows,  holds  the  key  from  being  sud- 


CLA.MP    FOIS    SETTING    TAl'l'KTS. 


denly  hurtled  out  of  the  key-way  by  the  blow  of  the  hammer.  After 
the  stem  has  been  adjusted  in  the  tappet,  this  second  man  ham- 
mers the  keys  back  into  place.  Where  the  tappets  are  bored  to  a 
close  fit  on  the  stems,  it  is  customary  for  one  man  to  loosen  the 
keys  slightly,  while  the  other  makes  a  quick  drive  at  one  of  the 
keys  when  the  tappet  has  slipped  to  the  mark ;  in  this  way  the  tap- 
pet setting  proceeds  rapidly.  A  chalk  mark  is  placed  around  the 
stem  above  the  tappet,  so  that  any  slipping  may  be  readily  noticed. 
If  the  tappets  stick  and  refuse  to  move,  a  little  kerosene  or  gaso- 
line may  be  poured  into  the  counter-bore  at  the  top  to  run  down 
between  the  stem  and  the  tappet,  while  the  tappet  is  struck  with 
a  hammer  on  the  inside  of  the  collar  or  on  the  waist.  The  outside 
or  wearing  face  must  never  be  roughened  by  being  struck,  or  the 
stamp  will  not  revolve  evenly  and  slowly  at  first  when  that  wear- 
ing face  is  put  into  use.  The  cam-stick  may  be  used  if  desired,  so 


50 


RIGHT   AND   LEFT-HAND   CAMS 


that  the  blow  of  the  cam  may  be  utilized  to  drive  the  tappet  upward 
on  the  stem  without  dropping  the  stamp  off  the  finger-jack.  When 
setting  tappets,  it  is  customary  to  hang  up  only  the  stamp  that  is 
being  set,  allowing  the  other  four  stamps  to  continue  dropping, 
with  the  possible  exception  of  when  setting  the  stamp  which  actu- 
ates the  feeder.  To  lessen  the  danger  to  fingers,  two  stamps  may 
be  hung  up,  the  one  being  set,  and  its  neighbor  on  the  side  next 
to  the  keys. 

Thick  tappet-keys  requiring  the  least  amount  of  shimming  and 
made  of  a  soft  steel,  with  the  ends  tempered  to  resist  the  blunting 


A    CLAMP   FOR    ATTACHING    CHAIN-BLOCKS    TO    STEM    WHICH    CAN    BE    PUT   ON 
ANYWHERE  WITHOUT   SLIPPING  OVER  END   OK   STEM. 


tendency  from  driving  the  keys  in  and  out,  will  be  found  the  most 
satisfactory. 

Cam. — The  cam  should  be  of  steel  to  insure  long  life  and  to  lessen 
the  chances  of  being  broken,  an  undesirable  occurrence  on  account 
of  the  labor  involved  in  replacing  with  a  new  cam.  They  are  set 
from  %  to  14  in.  away  from  the  stems,  which  is  as  close  as  the 
slight  longitudinal  play  of  the  cam-shaft  will  allow  them  to  be 
placed  without  occasionally  striking  or  rubbing  the  stem.  Cams 
are  called  'right-hand'  and  'left-hand,'  and  are  determined  by  the 
following  rule :  when  the  hub  of  the  cam  is  toward  the  observer 
and  the  cam  rotates  to  the  right,  or  clockwise,  it  is  a  'right-hand' 
cam ;  if  the  rotation  is  to  the  left,  or  counter  clockwise,  it  is  a  '  left- 
hand'  cam.  The  action  of  the  cams  upon  the  tappets  tends  to 
cause  the  cams  to  move  away  from  the  stamps.  This  lateral  thrust 
of  the  cams  and  cam-shaft  is  greatest  at  the  moment  when  each 
cam  leaves  its  tappet.  It  is  overcome  largely  in  the  10-stamp  cam- 
shaft by  making  the  cams  of  one  battery  left-hand,  and  those  of 
the  other  right-hand,  the  lateral  thrust  of  one  set  in  one  direction 
overcoming  that  of  the  other  set  in  the  other  direction.  With  a 


DESIGN    OF    CAM 


51 


five-stamp  cam-shaft  it  is  possible  to  use  two  right-hand  and  three 
left-hand  cams,  but  generally  the  boss  of  the  cam-shaft  pulley  is 
utilized  as  a  collar  in  connection  with  other  collars  to  prevent  the 
lateral  movement  of  the  shaft.  Even  with  the  10-stamp  cam-shaft 
there  is  a  constant  undesirable  longitudinal  shifting  of  the  shaft 
unless  collars  are  used. 

It  is  highly  important  that  the  cams  be  properly  designed  for 
the  speed  and  length  of  drop  to  be  used.     The  design  should  be 


LEFT-HAND    CAM. 

(Chrome  Steel  Works,  Chrome,  N.  J.) 

such  that  when  the  shoe  strikes  the  die  of  an  empty  mortar  the 
space  of  !/4  in.  or  more  will  intervene  between  the  faces  of  the 
tappet  and  the  cam,  near  the  hub  of  the  latter,  and  that  when  the 
stamp  has  reached  the  highest  point  of  its  rebound  from  striking 
the  die  the  cam  will  immediately  engage  the  tappet  at  a  low  but 
rapidly  increasing  speed  as  the  tappet  is  lifted  to  the  point  where 
it  drops  off  the  tip  of  the  cam.  One  of  the  greatest  sources  of 
noise,  wear  and  tear,  and  broken  parts,  arises  from  a  cam  improp- 
erly designed  and  which  suddenly  engages  or  violently  strikes  the 
tappet.  An  examination  of  tappets  in  mills  of  long  life  usually 


52  ROTATION    OP   STAMP 

shows  that  the  wearing  faces  or  shoulders  of  the  tappets  have  been 
worn  away  or  have  been  broken  through  inability  to  withstand 
severe  strains.  Makers  should  therefore  supply  tappets  with  extra 
thick  wearing  faces  or  shoulders,  and  the  waist  of  the  tappet  should 
be  cut  out  in  such  a  manner  that  the  projecting  shoulder  is  weak- 
ened as  little  as  possible. 

The  friction  of  the  cam  against  the  tappet  causes  the  stamp  to 
rotate  while  running.  This  is  necessary  that  the  face  of  the  tap- 
pet may  be  worn  smoothly  all  around,  and  also  that  the  shoes  and 
dies  may  wear  or  'cup'  evenly.  One  complete  rotation  of  the 
stamp  is  made  in  from  5  to  30  drops  of  the  present  style  of  stamps 
under  normal  conditions.  The  data  of  two  extreme  cases  will  give 
some  idea  of  the  cause  of  this  variation.  In  the  Gilpin  county 
practice,  a  stamp  weighing  550  lb.,  dropping  17  in.  thirty  times 
per  minute,  rotates  I1/-)  times  per  drop.  In  a  certain  mill  using 
1500-lb.  stamps,  dropping  6  in.  and  110  times  per  minute,  the  stamps 
make  one  complete  revolution  in  30  drops.  The  stamps  in  two 
mills  having  the  same  weight  of  stamps  and  the  same  adjustments, 
will  vary  in  their  speed  of  rotation,  due  to  different  shaped  cams 
and  to  the  amount  of  lubricant  on  them.  Where  the  stamps  rotate 
too  fast,  there  is  a  small  loss  of  power  and  too  much  wear  on  the 
cams  and  tappets.  This  twirling  of  the  stamps  may  be  caused  by 
the  wearing  parts  being  devoid  of  grease,  by  being  gritty  from 
dust,  by  being  roughened  through  running  without  grease,  or  by 
the  tappet  being  out  of  alignment  with  the  stem.  The  only  method 
of  stopping  the  twirling  is  to  apply  grease  to  the  face  of  the  cam; 
if  such  treatment  does  not  suffice  and  the  tappet  is  found  to  be 
warm,  the  stamp  should  be  hung  up  until  the  tappet  is  cold.  Twirl- 
ing is  most  prevalent  with  dusty  ore,  which  indicates  that  it  is 
due  to  dirt  and  lack  of  lubrication. 


CHAPTER  III 

STEM  AND  STEM  BREAKAGE — FASTENING  THE  STEM — ADJUSTING 
HEIGHT  OF  DROP — CAM-SHAFT  AND  CAM-SHAFT  Box — ORDER 
OF  DROP — STEM  GUIDE — FINGER  JACK — FEEDER — SCREEN. 

Stem  and  Stem  Breakage. — The  stem  was  formerly  made  of 
wrought  iron,  but  now  almost  always,  if  not  in  every  case,  of  mild 
steel.  The  stem  does  not  wear  out  directly,  but  indirectly  by  break- 
ing. These  breakages  occur  mainly  at  the  point  where  the  stem 
leaves  the  embrace  of  the  boss,  but  occasionally  an  old  stem  breaks 
near  the  tappet.  Breakages  at  other  points  so  seldom  occur  as  to 
be  phenomenal ;  in  fact,  breakages  near  the  tappet  are  almost  phe- 
nomenal from  their  infrequency,  so  that  it  is  customary  to  con- 


1!     • 

STAMP    STEM, 

(Traylor  Engineering  &  Manufacturing  Co.,  Allentown,  Pa.) 

sider  that  a  stem  will  break  only  at  the  boss.  When  the  stem 
breaks  at  the  boss,  it  is  reversed  and  the  other  tapered  end  is 
placed  in  the  socket  of  the  boss.  When  this  second  end  breaks,  the 
stem  is  sent  to  the  blacksmith-shop  to  be  swaged  down  again  at 
each  end,  or  to  the  lathe  to  be  turned  down,  after  which  it  is  re- 
turned to  the  mill  to  be  used  again.  After  so  many  breakages  have 
occurred  that  the  stem  will  no  longer  run  in  the  guides  from  being 
too  short,  a  new  piece  is  welded  to  it,  or  in  the  absence  of  facili- 
ties for  making  such  a  weld  the  stem  is  discarded.  After  welding, 
if  bent,  a  stem  may  be  straightened  by  laying  it,  while  still  hot, 
in  the  groove  between  two  old  stems  or  heavy  pipes,  of  a  diameter 
similar  to  the  stem,  placed  parallel  and  an  inch  apart  on  the  ground 
where  they  are  firmly  held  by  straps  or  bolts.  In  this  groove  the 
stem  may  be  hammered  and  straightened. 

The  breaking  of  stamp-stems  and  cam-shafts  has  been  popularly 
attributed  to  the  crystallization  of  the  metal;  the  theory  being 
that  the  continuous  jar  and  vibration  to  which  these  parts  are 

53 


54  CRYSTALLIZATION    OF   STEM 

subjected  causes  a  molecular  change  whereby  the  fibrous  structure 
of  the  metal  is  changed  to  a  granular,  crystalline  form,  which,  not 
having  the  tenacity  of  the  fibrous  structure,  finally  breaks.  Many 
arguments  have  been  advanced  for  and  against  this  theory,  but 
nothing  conclusive  has  been  shown.  It  is  pointed  out  that  the 
break  shows  an  apparently  crystalline  structure  because  it  is  across 
the  grain  of  the  metal  in  the  stem,  and  that  there  is  no  evidence 
to  show  that  any  change  takes  place  in  the  structure,  either  in 
the  case  of  a  broken  stamp-stem  or  in  any  experiment  made  in  a 
general  way.  It  is  also  pointed  out  that  should  crystallization  take 
place,  the  breaks  would  not  be  confined  so  generally  to  one  par- 
ticular point.  The  argument  has  been  presented  that  the  jar  and 
vibration  from  the  impact  of  the  shoe  upon  the  die  passes  into  the 
boss,  and  that  this  vibratory  motion  concentrates  to  pass  into  the 
small  cross-section  of  the  stem  at  the  point  where  the  stem  leaves 
the  boss,  and  here  is  the  point  of  greatest  stress.  Under  the  strain 
the  particles  of  metal  lose  their  power  of  cohesion;  the  metal  de- 
velops 'fatigue;'  minute  fractures  occur;  there  is  a  repeated  bend- 
ing stress  in  different  directions  from  the  stamp  striking  on  an 
uneven  surface,  as  when  a  piece  of  coarse  rock  is  lying  on  the  edge 
of  the  die ;  and  eventually  the  minute  fractures  develop  into  a 
break.  Conditions  prevail  in  the  stem  at  the  tappet,  where  the 
breaks  sometimes  occur,  somewhat  similar  to  those  at  the  boss. 
There  is  a  jar,  stress,  and  vibration  from  the  impact  of  the  cam 
upon  the  tappet  which  resembles  that  from  the  impact  of  the  shoe 
upon  the  die.  There  is  a  bending  strain  from  the  cam  striking  the 
side  of  the  tappet  and  away  from  the  centre  of  the  stem.  As  the 
tappet  is  continually  shifted  up  and  down  the  stem  and  its  em- 
brace is  such  that  the  vibratory  motions  are  not  communicated  to 
the  stem  so  constantly  at  one  point  as  at  the  boss,  the  strain  there 
is  less  and  breakages  do  not  frequently  occur. 

The  breaking  of  stems  can  be  prevented  by  annealing  them,  that 
is,  by  heating  and  slow  cooling.  This  fact  gives  color  to  the  theory 
that  crystallization  or  some  change  in  the  structure  of  the  metal 
does  take  place.  Annealing  is  usually  not  feasible,  except  when 
welding  or  repointing  the  stems.  It  is  carried  out  by  slowly  bring- 
ing the  stem  through  a  cherry  red  to  a  crimson  heat,  and  continu- 
ing at  that  heat  from  one  to  six  hours.  The  hot  stem  is  then  cov- 
ered with  hot  dry  ashes  so  that  the  cooling  may  be  as  slow  as  pos- 
sible. The  stems  are  sometimes  cooled  in  chloride  of  lime,  which 
is  an  exceptionally  poor  conductor  of  heat.  The  annealing  process 
does  not  fuse  or  weld  together  the  minute  fractures  in  the  stem, 


IRON   VS.    STEEL   STEMS  55 

but  relieves  the  stresses  and  strains  in  the  different  parts  of  the 
metal  which  are  developed  in  the  manufacture  of  the  stem  and 
greatly  increased  by  use  through  the  'fatigue'  of  the  metal.  The 
slower  the  cooling,  the  better  is  the  opportunity  for  the  strajns  to 
adjust  themselves.  Because  of  tendency  to  warp  unless  carefully 
performed,  it  is  generally  not  attempted  to  anneal  the  entire  stem, 
unless  they  break  elsewhere  than  at  the  boss.  The  breakages  have 
been  partly  prevented  by  boring  the  bosses  and  making  the  ends 
of  the  stems  larger.  It  is  a  question  among  millmen  whether  steel 
stems  break  less  frequently  than  those  made  of  iron.  In  general, 
they  do  break  less,  and  experiments  show  that  mild  steel  will  stand 
a  much  greater  strain  than  wrought  iron  before  breaking,  yet  in 
some  mills  where  both  iron  and  steel  stems  are  in  use,  the  iron 
has  been  found  superior.  This  is  because  the  steel  in  the  stems 
is  of  a  poor  quality  or  is  too  hard  and  brittle.  Manufacturers  find 
it  difficult  to  secure  supplies  of  the  high  quality  of  iron  requisite 
for  good  stems  and  cam-shafts.  The  essential  requirements  of  a 
good  stamp-stem  are  a  minimum  of  brittleness  and  tendency  to  crys- 
tallize and  fracture  under  constant  impact,  jar,  vibration,  and  bend- 
ing strain.  When  a  new  mill  having  stems  of  a  rather  poor  quality 
is  started,  the  breakages  will  comemnce  after  about  six  months  of 
running.  With  ordinarily  good  stems,  about  one  year  will  elapse 
before  the  breakages  begin.  The  breakages  may  be  expected  with 
steady  frequency  after  the  first  occurrence  with  a  set  of  stems. 
The  frequency  of  the  breakages  or  the  life  of  the  stems  will  vary 
with  each  maker,  sometimes  with  each  set  from  the  same  maker. 
It  is  interesting  to  note  this  fact  when  two  sets  of  stems  are  being 
used  in  the  same  mill.  In  one  instance  in  an  enlarged  mill,  the 
iron  stems  of  the  old  part  of  the  mill  broke  with  a  frequency  that 
indicated  an  average  life  for  each  stem  of  seven  years  between 
breaks,  while  the  steel  stems  in  the  new  part  of  the  mill  averaged 
about  one  year  of  use  between  breaks.  In  this  case  the  trouble  due 
to  stems  pulling  out  of  their  bosses  was  practically  seven  times  as 
great  in  the  new  mill  section,  since  when  the  two  parts  are  first  put 
together  there  is  some  doubt  as  to  whether  they  will  hold  perma- 
nently, and  the  longer  they  have  held  together  the  less  tendency 
there  is  for  them  to  pull  apart.  It  is  a  very  good  stem  that  will 
average  three  years  of  use  between  breaks. 

With  a  view  to  reducing  the  bending  strain  and  causing  less 
wrenching  of  the  stem  when  striking  an  uneven  surface,  stamps 
have  been  designed  in  which  the  centre  of  gravity  is  placed  as 
low  as  possible.  Both  guides  are  bored  to  a  close  fit  on  the  stem, 


56  STEM    PULLING   OUT   OF   BOSS 

with  the  lower  guide  placed  near  the  boss.  The  stem  is  made  short, 
using  a  long  boss  to  make  up  the  required  weight,  the  result  being 
that  the  stem  drops  straight  and  true,  and  that  there  is  a  minimum 
of  bending  and  wrenching  when  the  shoe  strikes  away  from  the 
centre  line  of  the  stamp.  The  results  with  these  stamps  appear  to 
demonstrate  the  correctness  of  the  theory  upon  which  they  are 
built. 

Running  the  stamps  with  the  feed  too  low  or  the  mortar  empty — 
'pounding  steel' — shortens  the  life  of  the  stems.  The  same  may  be 
said  of  poor  and  irregular  feeding.  When  a  piece  of  vagrant  steel 
lodges  on  the  top  of  a  die,  as  is  usually  the  case  when  a  stamp 
suddenly  begins  to  drop  harder  and  shorter  than  its  neighbors  in 
the  same  battery,  it  should  be  removed  or  it  may  cause  the  stem 
to  break.  A  die  tipping  over  in  the  mortar  will  cause  the  stamp 
to  act  in  the  same  way  and  will  be  productive  of  the  same  evil 
result.  Concrete  mortar-blocks  were  formerly  supposed  to  be  more 
severe  on  stems  than  wooden  blocks,  but  the  results  in  good  in- 
stallations, where  everything  is  kept  solid  and  tight,  disprove  this. 

Overfeeding  the  motar  causes  the  shoes  to  come  off,  and  millmen 
popularly  ascribe  it  to  the  suction  of  the  deep  body  of  dense  pulp 
through  which  the  shoe  is  moving.  It  may  also  be  due  in  a  nar- 
row mortar  to  coarse  rock  wedging  between  the  shoe  and  the  side 
of  the  mortar,  and  thus  forcing  the  shoe  off.  Another  view  when 
overfeeding  is  that  the  falling  stamp  is  halted  by  the  overthick 
bed  of  pulp,  so  that  the  cam  does  not  come  in  contact  with  the 
tappet  in  the  usual  way  with  a  light  force,  but  strikes  the  tappet 
a  severe  blow  as  the  two  come  in  contact  at  a  point  where  the 
peripheral  speed  of  the  cam  is  high.  This  is  similar  to  camming, 
and  tends  to  loosen  the  shoe  from  the  bosshead  and  the  bosshead 
from  the  stem.  When  the  speed  becomes  dangerously  high  for  a 
fraction  of  a  minute,  as  when  the  engine  governor  does  not  act 
promptly,  or  as  often  happens  with  electric  power  at  night,  the 
resulting  camming — and  in  fact  camming  under  any  condition — 
tends  to  loosen  the  shoes,  and  principally  to  loosen  bossheads  and 
break  stems  as  well  as  cams  and  cam-shafts. 

Fastening  the  Stein. — In  putting  stems  into  bosses,  the  boss,  with 
or  without  the  shoe,  should  rest  on  the  die  and  not  on  a  thick  bed 
of  pulp.  The  boss  should  be  placed  exactly  underneath  the  stem, 
which  should  be  raised  just  sufficiently  to  allow  this  or  to  give  the 
right  height  of  drop  after  the  parts  are  fastened.  Two  strips  of 
canvas,  2  in.  wide  by  15  in.  or  more  long,  should  be  placed  across 
the  socket  of  the  boss  at  right  angles  to  each  other  and  slightly 


FASTENING   STEM    IN   BOSS  57 

pushed  in.  The  stem  is  now  dropped  off  the  finger- jack  into  the 
socket  of  the  boss  by  means  of  the  cam-stick,  and  is  allowed  to  be 
dropped  by  the  revolving  cams  until  the  boss  is  caught  and  the 
stem  driven  in.  The  stamp  should  be  rotated  while  dropping  so 
that  the  stem  may  be  driven  straighter  into  the  boss.  Another 
method  of  dropping  the  stem  into  the  socket  of  the  boss  is  to  loosen 
the  tappet  and  raise  the  stem  by  the  chain-blocks,  then  tap  with 
a  hammer  upon  the  clamp  or  chain  by  which  the  chain-blocks  are 
hooked  to  the  stem ;  this  will  jar  the  clamp  loose,  so  that  the  stem 
will  slip  through  and  into  the  socket  of  the  boss.  Care  must  be 
exercised  to  have  the  boss  placed  properly  and  to  see  that  the 
guides  are  tight,  so  that  the  stem  may  drop  directly  into  the  socket 
instead  of  striking  on  top  of  the  boss.  A  chalk  mark  is  placed 
near  the  end  of  the  stem  to  indicate  just  how  far  it  can  be  allowed 
to  enter  the  boss,  since  should  it  enter  too  far,  it  would  be  impos- 
sible to  insert  the  'drift'  for  driving  out  the  'plug'  or  broken 
stem-end,  should  the  stem  break  again.  Some  bosses  have  a  hole 
running  through  the  centre ;  by  removing  the  shoe,  a  steel  bar  may 
be  inserted  in  this  hole  to  enable  the  broken  stem-end  to  be  driven 
out.  The  stem  may  be  lowered  into  the  socket,  and  should  it  appear 
that  it  will  enter  too  far,  more  strips  of  canvas  should  be  used. 
It  is  a  practice  with  many  millmen  to  lower  the  stem  into  the 
socket  and  drive  it  in  by  pounding  with  a  heavy  hammer  on  the 
upper  end.  This  should  never  be  permitted,  as  it  is  certain  to  spoil 
the  tapered  end  so  that  it  will  not  fit  well  in  the  socket  when  re- 
versed, or  should  it  be  a  broken  end,  it  will  'mushroom'  into  a 
jagged  end  over  which  a  tappet  cannot  be  slipped. 

When  a  stem  pulls  out  of  a  boss  and  runs  for  some  time  before 
being  seen  and  hung  up,  the  tapered  end  is  usually  pounded  out 
of  shape  to  fit  the  socket,  though  it  may  not  be  apparent  to  the 
eye.  If  the  stem  will  not  catch  again,  it  should  be  hoisted  out  of 
the  mortar  and  allowed  to  rest  on  a  plank  across  the  top  of  the 
mortar,  where  it  can  be  chipped  and  dressed  with  cold  chisels  and 
files.  It  is  reported  that  some  millmen  do  not  turn  their  broken 
stems,  but  that  two  men  dress  down  the  broken  end,  using  cold 
chisels  with  wooden  handles  and  double-hand  hammers;  it  is  doubt- 
ful if  a  satisfactory  job  could  be  done,  unless  the  required  taper 
is  slight. 

Canvas  should  always  be  placed  in  the  sockets,  as  it  will  lessen 
the  number  of  breakages.  When  steel  is  wedged  tightly  against 
steel,  it  becomes  as  if  made  of  one  piece,  and  all  the  jar  and  vibra- 
tory motion  is  communicated  to  the  stem  at  the  point  where  it 


58  CHANGING    STEMS 

leaves  the  embrace  of  the  boss.  By  placing  canvas  between  the 
parts,  the  tendency  is  for  the  jar  and  vibration  to  be  more  gener- 
ally distributed,  instead  of  concentrated  at  one  point.  Likewise, 
the  distribution  of  the  bending-strain  may  be  over  a  larger  area. 
While  canvas  causes  the  parts  to  hold  together  as  well  or  better 
than  if  not  used  through  acting  as  a  filler  of  small  spaces  where 
the  stem  and  boss  are  not  in  a  perfect  wedging  contact,  it  allows 
the  stem  or  broken  end  to  be  removed  more  easily  by  the  usual 
means  of  drifting,  or  blowing  out  with  dynamite.  Where  it  is  not 
used,  the  parts  tend  to  rust  together  so  that  sometimes  a  boss  is 
blown  to  pieces  in  the  effort  to  remove  it  from  the  stem.  When 
canvas  fails  to  make  the  stem  stick,  a  shim  made  of  tough  metal 
should  be  tried,  such  as  a  thick  screen  plate,  or  thin  sheet  iron, 
bent  cylindrically  and  set  in  the  socket ;  or  the  metal  may  be  cut 
in  strips  arid  shaped  to  fit  in  the  socket  in  the  same  manner  as  can- 
vas strips.  If  the  stem  still  fails  to  stick,  it  may  be  that  the  taper 
does  not  fit  the  socket  and  requires  dressing  down ;  or  both  the 
stem  and  the  socket  may  be  too  smooth  to  catch  and  bind,  in 
which  case  a  small  stream  of  some  fine  grit,  such  as  jasper,  should 
be  allowed  to  run  into  the  socket  with  the  stem  rising  and  falling 
so  that  the  surfaces  may  be  roughened  and  eventually  bind  on  one 
another,  or  the  surfaces  may  be  roughened  by  denting  with  chisels. 
Some  stems  will  refuse  to  hold  in  the  bosses,  requiring  the  utmost 
patience  before  being  finally  fastened.  The  difficulty  may  generally 
be  ascribed  to  the  taper  of  the  stem  not  corresponding  to  the  bore 
of  the  boss,  either  from  the  way  it  was  first  fashioned  or  from  being 
pounded  out  of  shape.  As  a  result,  the  binding  surface  between  the 
stem  and  the  boss  is  small — the  stem  may  only  shoulder  against 
the  boss  with  a  minimum  of  the  wedging  effect.  Naturally,  the 
remedy  is  to  shape  and  dress  down  the  tapered  end  until  it  holds. 
The  last  resort,  if  the  stem  will  not  catch,  is  to  turn  the  stem  or 
put  in  another  boss.  Stems  are  fastened,  whenever  possible,  through 
the  top  of  the  mortar  without  stopping  the  other  stamps. 

When  a  stem  breaks,  the  first  thing  to  do  is  to  hang  it  up  on 
the  finger-jack,  allowing  the  others  to  run  until  ready  to  change 
this  stem ;  should  this  not  be  for  some  time,  the  boss  with  its  shoe 
should  be  removed  from  the  mortar.  When  ready  to  change  the 
stem,  the  battery  is  'pounded  out'  or  'stamped  out,'  which  con- 
sists in  shutting  off  the  feed  and  allowing  the  stamps  to  run  as  long 
as  may  be  safe,  so  as  to  remove  as  much  pulp  as  possible  from  the 
mortar,  the  feed-water  being  shut  off  just  before  hanging  up  the 
stamps  that  the  mortar  may  also  be  empty  of  water.  The  screen 


REMOVING    BROKEN    STEM-END  59 

is  removed,  together  with  the  chuck-block,  and  the  boss  is  inclined 
outward  from  the  mortar,  the  'drift'  is  then  inserted  in  the  key- 
way  and  the  broken  stem-end  driven  out,  after  which  the  boss  is 
righted  into  its  place.  Where  the  mortar-opening  is  too  small 
vertically  to  allow  the  boss  to  be  thus  righted  into  its  place,  as  is 
liable  to  be  the  case  with  a  boss  having  a  new  shoe  or  with  the  long 
bosses  of  heavy  stamps,  a  small  rope-block  is  attached  to  the  lower 
battery-girt  and  extended  down  through  the  top  of  the  mortar,  and 
the  boss  and  shoe  are  pulled  into  position,  after  which  the  mortar 
is  closed  and  the  other  stamps  are  started  dropping.  Open-front 
mortars  were  designed  for  the  express  purpose  of  obviating  this 
trouble.  Two  or  more  turns  of  a  stout  chain  are  now  taken  about 
the  tappet  of  the  broken  stem,  and  the  chain-blocks  hooked  into  this 
chain.  The  stem  is  raised  until  the  tappet  nearly  touches  the  upper 
battery-girt.  The  battery  is  now  hung  up  and  the  power  thrown 
off  from  the  cam-shaft.  Both  the  upper  and  lower  guides,  which 
have  been  previously  loosened,  are  now  removed,  and  the  stem  and 
tappet  are  swung  clear  of  the  battery-girt.  Raising  of  the  stem  is 
continued  until  it  is  possible  to  swing  the  lower  end  out  on  the 
cam-floor.  If  it  is  only  desired  to  reverse  the  stem,  it  can  now  be 
done  and  returned  to  its  place;  but  should  it  be  desired  to  put  in 
a  new  stem — one  having  a  tappet  held  in  place  by  one  key  lightly 
driven  in  usually  being  on  hand  for  such  cases — the  old  one  is 
lowered  to  the  floor,  and  the  new  one  is  picked  up  and  swung  into 
place.  As  soon  as  the  stamp  is  swung  into  position,  the  other  stamps 
of  the  battery  are  started  dropping.  The  guides  are  put  back  and 
the  tappet  is  temporarily  adjusted  for  fastening  the  stem  in  the  boss, 
as  explained  before. 

Some  men  are  able  to  turn  or  change  a  stem  without  stopping 
the  cam-shaft  and  the  other  stamps,  but  it  is  so  dangerous  to  limb, 
life,  and  machinery  that  it  should  not  be  attempted.  If  the  plug 
does  not  easily  drift  out  of  the  boss,  the  boss  is  removed  to  a  more 
convenient  spot  for  driving  the  'drift,'  or  a  new  boss,  together  with 
the  old  shoe,  is  used.  Blowing  the  plugs  out  with  dynamite  is  a 
lazy  man's  refuge  and  may  split  the  boss,  especially  when  made  of 
iron;  though  it  is  reported  that  even  tight  keys  between  cam-Shafts 
and  cams  or  cam-shaft  pulleys  have  been  blown  out  by  dynamite. 
The  careful  millman  will  start  with  very  small  charges  of  dynamite 
and  increase  them  until  the  parts  are  loosened.  He  will  also  see  that 
the  dynamite  is  in  contact  with  the  part  to  be  blown  out.  The  use 
of  dynamite,  besides  breaking  parts  and  developing  minute  fractures 
which  later  break,  causes  the  mill  parts  to  be  jarred  loose  and  jars 


60  ADJUSTING   HEIGHT   OF   DROP 

the  mill  generally  so  that  dust  settles  in  the  bearing  parts.  At  one 
mill  where  trouble  has  been  experienced  from  the  plugs  not  readily 
drifting  out,  the  boss  is  heated  until  the  canvas  chars,  when  the 
plug  will  drift  out  easily.  In  fact,  heating  the  boss  to  cause  it  to 
expand,  will  enable  a  tight  plug  to  be  removed  easily,  even  where 
canvas  has  not  been  used. 

Adjusting  Height  of  Drop. — It  is  customary  to  allow  the  stamps 
to  increase  their  height  of  drop  through  the  wearing  away  of  the 
shoe  and  die,  from  %  to  1  in.  before  re-setting.  There  are  several 
ways  of  measuring  the  height  of  drop  and  the  amount  it  must  be  de- 
creased. One  way  is  to  open  the  mortar  and  measure  the  distance 
between  each  shoe  and  its  die.  This  is  an  impractical  way,  requiring 
too  much  labor,  while  the  measurements  are  unreliable  if  taken  from 
a  spot  in  the  die  that  has  cupped  unevenly,  or  if  the  finger-jacks 
are  of  an  uneven  height. 

Another  method  of  measuring  the  height  of  drop  is  to  hold  a 
piece  of  metal,  such  as  the  shims  used  with  tappet-keys,  against  the 
stem  at  the  guide  and  measure  the  scratch-marks  on  the  grease 
with  a  rule  while  stamp  is  running;  or  chalk-marks  may  be  quickly 
placed  on  the  stem  at  top  of  the  guide  when  the  stamp  strikes  the 
die,  and  the  lift  of  the  stamp  measured  in  the  same  as  with  the 
scratch-marks.  The  measurements  obtained  in  these  ways  are  also 
liable  to  be  inexact.  A  better  method  is  to  hang  up  each  stamp, 
rub  off  some  of  the  surplus  grease  above  the  upper  guide,  and  oil 
the  upper  guide  well  before  dropping  the  stamp.  After  all  the 
stamps  in  a  battery  have  been  treated  in  this  way,  hang  up  the  feed- 
stamp  or  shut  off  the  feed  as  long  as  safe.  The  oil-marks  will  now 
show  the  exact  relative  drop  of  each  stamp  when  they  are  hung  up. 
Should  the  finger-jacks  be  uneven,  the  oil-marks  should  be  measured 
while  the  stamps  are  running.  The  tappets  can  be  set  by  these  oil- 
marks  and  re-checked  after  dropping  again. 

The  best  method  of  adjusting  the  height  of  drop  is  for  the  millman 
to  examine  the  stamps  once  daily,  and  by  his  experienced  eye  single 
out  those  stamps  that  are  dropping  too  long  and  too  hard.  Laying 
his  fingers  on  the  tappets  or  stems,  he  feels  these  stamps  striking 
harder  than  their  neighbors  in  the  same  battery,  and  in  consequence 
he  reduces  their  drop  */£  in.  He  does  not  attempt  to  have  each  stamp 
drop  the  same  exact  distance  or  any  exact  distance  in  relation  to 
the  other  stamps,  since  when  using  the  methods  first  mentioned,  the 
drop  of  the  middle  or  end  stamps  is  often  varied  a  certain  amount 
to  get  a  more  even  stamping  effect.  He  aims  to  have  the  individual 
stamps  of  a  battery  strike  with  an  equal  firmness,  so  that  all  may 


IRON  VS.  STEEL  FOR  THE  CAM-SHAFT  61 

have  an  equal  or  maximum  crushing  effect,  and  so  that  he  may  be 
able  to  feed  the  battery  down  to  a  point  where  the  greatest  amount 
of  crushing  effect  can  be  obtained.  He  also  aims  to  run  with  the 
maximum  of  drop  permissible  with  the  speed  set.  These  are  some 
of  the  secrets  of  getting  a  large  tonnage  through  a  battery,  and 
attention  to  them  may  result  in  increasing  the  capacity  from  10  to 
20%,  as  against  a  battery  in  which  one  stamp  comes  down  hard, 
while  its  neighbor  is  cushioned,  or  where  the  drop  is  not  kept  as  long 
as  possible  within  limits  of  safety. 

The  inside  of  the  mortar  should  be  occasionally  examined  to  ascer- 
tain how  the  shoes  and  dies  are  wearing,  and  also  to  look  for  any 
fragments  of  broken  steel  that  may  have  fallen  in,  or  have  come  in 
with  the  ore.  This  latter  should  always  be  attended  to  when  chang- 
ing screens. 

Cam-Shaft  and  Cam-Shaft  Box. — The  cam-shaft  is  of  hammered 
wrought  iron  or  of  hammered  mild  steel,  with  an  increasing  tendency 
to  use  iron  shafts.  A  material  is  required  for  stems  and  cam-shafts 
that  is  tough  rather  than  brittle,  and  is  able  to  withstand  the 
tendency  to  crystallize  and  break  under  impact;  a  good  grade  of 
wrought  iron  will  answer  these  requirements  as  well  or  better  than 
steel.  It  is  the  experience  of  most  millmen  that  mills  having  iron 
cam-shafts  have  very  little  trouble  from  the  breaking  of  the  same, 
and  that  the  substitution  of  iron  shafts  where  steel  ones  break  fre- 
quently will  give  great  satisfaction;  though  as  noted  in  connection 
with  stamp  stems,  it  is  the  grade  of  the  material  and  its  peculiar 
fitness  for  the  conditions  under  which  it  is  to  work  that  determine 
what  satisfaction  it  will  give.  Cam-shafts  break  from  the  same  cause 
as  stems,  from  'fatigue'  and  crystallization  of  the  metal,  and  from 
the  extension  of  minute  fractures  formed  coincidently  with  'fatigue' 
and  crystallization,  or  through  defective  manufacture  or  severe  wear 
and  tear  and  camming.  The  main  cause  is  the  impact  of  the  cams 
upon  the  tappets,  and  in  a  poorly  constructed  mill,  where  the  bat- 
tery-posts jump  and  vibrate  and  are  out  of  line,  by  pounding  in  the 
bearing  boxes.  The  breaking  of  a  cam-shaft  is  a  serious  thing  as 
compared  with  the  breaking  of  a  stem,  since  it  involves  considerable 
time  and  labor,  and  usually  a  complete  loss  of  the  cam-shaft.  It 
was  customary  to  make  the  shafts  for  the  lighter  stamps  from  4!/o  to 
5  in.  diam.  As  the  weight  of  stamps  has  increased,  the  diameter 
of  the  cam-shafts  has  not  always  correspondingly  increased,  and  this 
has  been  one  cause  of  shafts  breaking.  A  10-cam  shaft  for  1000-lb. 
stamps  should  be  6  in.  or  more  in  diameter,  14  to  15  ft.  long,  and 
will  weigh  upward  of  1400  Ib.  For  1250-lb.  stamps  a  shaft  7  in.  diam. 


62 


CAM-SHAFT    BREAKAGE 


and  weighing  1800  Ib.  or  more  should  be  used.  Five-cam  shafts  do 
not  require  to  be  so  large  in  diameter  for  the  same  weight  of  stamps 
as  10-cam  shafts.  With  the  10-cam  shafts  now  in  use  there  are  three 
bearings.  These  get  out  of  alignment  by  the  shifting  of  the  battery- 
frame  and  the  great  wear  and  tear  peculiar  to  a  stamp-battery, 
which  tends  to  throw  the  weight  and  stress  on  two  boxes  or  bear- 
ings, making  too  great  a  strain  for  a  long  shaft,  so  that,  as  the  shaft 
becomes  weakened  from  the  'fatigue'  or  crystallization  of  the  metal, 


LEFT  HAND  CAMS  -RK3HT  HAND  CAMS 

10-Stamp  Shaft   with  Pulley  on  Right  of  Mill. 


LEFT  HAND  CAMS  RIGHT  HAND  CAM 

10-Stamp  Shaft  with  Pulley  on  Left  of  Mill. 


CAM-SHAFTS 

(Traylor  Engineering  &  Manufacturing  Co.,  Allentown,  Pa.) 

it  is  liable  to  break,  especially  when  a  stamp  is  camming  on  it  near 
a  non-supporting  bearing.  The  bearing-boxes  should  be  securely 
bolted  to  the  battery-posts,  and  when  the  shaft  commences  to  throw 
out  puffs  of  air  from  the  boxes,  or  to  '  thrash, '  pound,  heat,  or  vibrate 
in  them,  they  should  be  immediately  babbitted  that  they  may  be  in 
exact  alignment  and  have  three  good  bearings.  If  cast-iron  boxes 
without  babbitt  are  in  use,  the  shaft  should  be  removed  and  these 
boxes  aligned.  No  shimming  should  be  used  under  them  as  it  will 
work  loose  from  the  jar  about  a  battery.  And  it  would  appear 


FIVE-STAMP   CAM-SHAFT  63 

unnecessary  to  state  that  only  a  most  secure  and  solid  construction 
that  would  be  least  liable  to  allow  any  movement,  change,  or  wear 
in  the  cam-shaft  bearings  is  what  is  necessary ;  that  any  construction 
giving  a  cushioning  or  spring  effect  must  sooner  or  later  cause 
serious  trouble. 

There  is  a  great  advantage  in  using  5-cam  shafts  in  that  there  are 
few  or  no  breakages.  As  there  are  but  two  bearings,  even  if  the 
boxes  do  get  out  of  line  there  is  no  abnormal  strain  at  any  time. 
These  shafts  enable  one  battery  to  be  shut  down  to  change  a  stem 
or  for  working  on  the  interior  of  a  mortar  without  interfering  with 
the  operation  of  another.  The  disadvantages  are  a  slight  increase 
in  the  length  of  the  mill  and  the  power  required,  also  a  doubling  of 
the  number  of  battery  belts,  pulleys,  and,  in  some  mills,  the  belt- 
tighteners.  There  is  also  the  lateral  thrust  of  the  cam-shafts  in  one 
direction,  but  this  is  successfully  met  by  the  use  of  collars.  The 
two-piece  or  sectional  collar  will  be  found  superior  to  the  single- 
piece  collar,  as  it  has  a  clamping  effect  in  addition  to  that  of  the 
set-screws,  and  can  be  easily  and  conveniently  put  on  or  removed. 
A  South  African  mill  of  160  stamps  was  built  with  fourteen  10-stamp 
cam-shafts  and  four  5-stamp  cam-shafts,  that  the  10-stamp  shafts 
that  broke  might  be  utilized  as  5-stamp  shafts. 

Where  there  is  a  minimum  of  jar  in  the  battery-posts,  and  the 
bearing-boxes  are  not  liable  to  get  out  of  line,  cast-iron  cam-shaft 
boxes  are  the  best,  as  there  is  no  loss  of  time  in  babbitting,  and  little 
trouble  from  the  shaft  getting  out  of  alignment  or  from  having  an 
abnormal  strain  due  to  the  wearing  and  breaking  away  of  the  babbitt. 
Where  there  is  much  vibration  of  the  battery-posts,  babbitt,  being 
a  softer  metal,  is  preferred  for  holding  the  shaft,  while  the  frequent 
re-babbittings  serve  for  aligning  the  shaft  anew.  Yet  the  truth  of 
the  matter  is  that  if  there  is  much  vibration  and  pounding  of  the 
shafts,  the  babbitt  is  soon  worn  out  or  is  broken  and  may  fall  into 
the  mortar  and  foul  the  amalgamation.  In  such  cases  it  is  better  to 
repair  the  battery  and  substitute  iron  ^boxes.  The  iron  boxes  are 
being  placed  in  new  mills  and  substituted  in  old  mills  when  repairs 
are  required. 

To  babbitt  the  boxes,  the  shaft  is  raised  by  means  of  screw-jacks, 
chain-blocks,  or  preferably  by  two  long  pieces  of  timber  used  as 
levers.  The  old  babbitt  is  knocked  out  by  means  of  chisels,  when  the 
shaft  is  let  down  into  the  position  in  which  it  shall  run  and  is 
leveled.  Cardboard  luted  with  clay  is  placed  about  the  shaft  at  the 
ends  of  the  boxes,  so  that  the  molten  metal  may  not  run  out.  The 
melted  babbitt  is  now  poured  in,  and  as  soon  as  cold  the  clay  is  re- 


64 


BABBITTING    CAM-SHAFT    BOXES 


moved,  and  also  the  timber  or  other  supports  to  the  shaft,  after 
which  the  shaft  is  started  revolving  and  the  stamps  to  dropping. 
Should  the  babbitt  give  trouble  by  breaking,  especially  in  the  box  at 
the  opposite  end  of  shaft  from  the  pulley  where  the  shaft  will 
'thrash'  about  the  most,  it  should  be  softened  by  adding  some  lead 
in  the  melting.  It  is  well  to  have  on  hand  a  set  of  half-rings  made 
of  iron.  These  are  inserted  at  each  end  of  the  boxes,  and  the  shaft 
is  lowered  on  them  and  made  perfectly  level,  after  which  the  sup- 
ports are  removed.  The  rings  serve  to  hold  the  shaft  in  position 
while  the  babbitt  is  being  poured  in  and  to  make  the  shell  of 
babbitt  of  the  right  thickness.  It  may  also  be  necessary  to  use  the 


CANDA    SELF-TIGHTENING    CAM. 

The  studs  upon  the  cam-shaft  are  pins  driven  into  holes  drilled  1  in.  deep 

into  the  shaft. 
(Chrome  Steel  Works,  Chrome,  N.  J.) 


clay  to  keep  the  molten  babbitt  from  running  out.  After  the 
babbitt  has  set,  the  rings  are  pried  out.  Iron  caps  for  these  bear- 
ings are  universally  discarded,  except  on  the  outward  bearing  of 
5-stamp  cam-shafts,  but  dust-caps  of  canvas  should  always  be  used. 
When  a  10-eam  shaft  breaks,  running  is  continued  with  5  stamps 
if  possible,  until  ready  to  remove  the  shaft.  The  stamps  are  then 
raised  by  the  chain-blocks  until  a  6-in.  block  can  be  slipped  between 
each  tappet  and  its  finger-jack.  This  'permits  the  shaft  to  be  raised 
by  levers,  screw-jacks,  or  chain-blocks — first  with  chain-blocks  re- 
moving the  pulley  or  bull-wheel,  to  be  rolled  out  on  timbers  away 
from  the  boxes.  If  self-tightening  cams  are  used,  they  are  re- 
moved, as  it  is  only  necessary  to  strike  them  with  a  hammer  on 


REMOVING  A  BROKEN  CAM-SHAFT  65 

the  point  in  the  reverse  way  to  which  they  run.  The  broken  shaft 
is  taken  away  and  a  new  one  is  brought.  The  cams  are  placed  on 
this  shaft,  and  it  is  then  rolled  and  lowered  into  place.  If  the 
old-fashioned  cams,  fastening  with  keys  in  a  slot  cuf  in  the  shaft, 
are  used,  the  shaft  and  cams  are  at  once  removed  from  the  mill  and 
a  new  shaft,  having  a  full  set  of  cams  in  position,  is  placed  in  the 
bearings.  This  method  is  necessitated  by  the  fact  that  to  remove 


CAM-SHAFT   WITH   BLANTON   SELF-TIGHTENING   CAMS. 

(Union  Iron  Works  Co.,  San  Francisco.) 

and  to  replace  a  set  of  keyed  cams  is  a  long  and  laborious  process. 
The  fastening  clips  of  self-tightening  cams  should  be  of  brass^,  for 
the  cams  are  more  difficult  to  loosen  when  the  clips  are  of  a  material 
that  will  rust.  Heating  the  boss  of  the  cam  with  a  brazing  torch 
assists  in  loosening  a  tight  cam,  either- of  the.  keyed  or  self-tighten- 
ing type. 

Order  of  Drop. — The  order  of  drop  of  the  stamps  in  a  battery 
should  be  such  that  an  even  bed  of  pulp  is  kept  over  the  dies, 
rather  than  an  excess  over  one  die  and  too  little  over  another,  and 


66  ORDER  OF  DROP 

that  the  splashing  or  wave  motion  of  the  pulp  be  produced  evenly 
along  the  screen.  The  first  has  reference  to  the  crushing  capacity 
of  a  battery,  while  the  second  refers  to  its  screening  efficiency,  the 
two  factors  that  make  for  tonnage.  The  academic  requirement 
that  no  two  adjacent  stamps  shall  drop  consecutively,  or  in  simpler 
language,  that  no  two  stamps  side  by  side  shall  follow  each  other 
in  dropping,  is  fulfilled  by  only  one  order,  1-3-5-2-4,  or  its  reverse 
which  is  usually  spoken  of  as  1-4-2-5-3,  since  the  custom  in  number- 
ing is  to  face  the  front  of  the  mortar  and  to  consider  the  first  or 
end-stamp  on  the  left  as  dropping  first.  Another  order  of  drop 
and  the  one  which  is  most  popular  with  practical  millmen  is 
1-5-2-4-3.  It  will  be  noticed  that  the  third  stamp  follows  the 
fourth  in  dropping.  The  reverse  of  this  drop  as  determined  by 
counting  it  from  the  rear  of  the  mortar  and  then  applying  it  to 
the  front  is  1-4-2-3-5,  in  which  the  third  stamp  follows  the  second 
in  dropping. 

Practically  every  conceivable  order  of  drop  has  been  used,  but 
the  above  two  systems  are  the  only  ones  that  have  stood  the  test  of 
time.  Much  confusion  exists  in  speaking  or  writing  of  the  different 
orders  of  drop.  Thus  one  man  will  say  that  1-3-5-2-4  is  a  good  order 
and  has  been  found  to  be  satisfactory,  and  that  1-4-2-5-3  has  been 
found  to  be  a  poor  order  and  unsatisfactory.  Since  the  latter  is 
the  reverse  of  the  first,  it  is  difficult  to  understand  how  it  could  be 
better  or  worse. 

The  1-5-2-4-3  order  has  been  found  superior  to  the  1-3-5-2-4,  both 
generally  and  where  they  have  been  tested  against  each  other.  A 
case  under  observation  will  illustrate  the  difficulties  and  the 
disadvantages  of  the  1-3-5-2-4  order.  There  was  in  use  a  narrow 
mortar  and  a  1000-lb.  stamp  dropping  103  times  per  minute  through 
a  distance  of  7  to  8  in.  As  long  as  the  height  of  discharge  was  kept 
as  tlow  as  possible,  and  the  feed  perferably  of  coarse  rock,  little 
trouble  was  experienced.  The  tendency  of  the  pulp  to  bank  under 
the  first  stamp  and  leave  the  fifth  pounding  was  marked,  but  m 
proportion  as  the  feed  was  kept  low  and  the  stamps  almost  'pound- 
ing steel,'  this  trouble  was  overcome.  As  the  height  of  discharge 
was  raised  and  finer  rock  was  fed  to  the  mortar,  the  trouble  from 
the  pulp  swinging  toward  the  first  stamp  became  so  great  that 
when  attempting  to  do  fine  crushing  by  the  use  of  a  high  discharge 
and  a  fine  screen,  the  results  were  most  unsatisfactory,  both  as  to 
tonnage  and  operation.  The  first  stamp  was  set  to  drop  8  in.  and 
the  others  evenly  graded  down  to  41/->  in.  on  the  fifth  stamp,  but 
without  getting  the  stamps  to  strike  a  blow  of  equal  hardness.  The 


WOOD   VS.    IRON   GUIDES  6? 

pulp  discharged  from  the  third,  fourth,  and  mainly  from  the  fifth 
stamp,  so  that  it  was  necessary  to  improvise  a  distributing  box  tc 
get  an  even  distribution  across  the  plates.  This  difficulty  with  the 
1-3-5-2-4  order,  when  running  with  a  medium  or  high  discharge,  is 
generally  reported,  and  it  cannot  be  considered  as  a  satisfactory 
order  for  fine  screening,  or  a  soft  ore,  or  a  high  discharge. 

The  1-5-2-4-3  order  gives  a  more  even  splash  across  the  screen  and 
a  better  distribution  in  the  mortar;  consequently  it  gives  a  higher 
capacity  with  less  trouble  in  operating.  An  increase  in  capacity 
has  been  reported  of  as  high  as  29  %  by  changing  to  this  order  of 
drop  from  the  other  one  mentioned.  It  scours  more  severely  in  the 
centre  of  the  mortar  than  the  other  order,  so  that  it  is  harder  on 
the  screen  and  chuck-block  at  this  point. 

While  strongly  recommending  that  the  1-5-2-4-3  order  be  used, 
it  is  advisable  that  the  millman  be  able  easily  to  change  to  the 
1-3-5-2-4  and  thus  try  both.  The  mills  built  today  are  all  supplied 
with  self-tightening  cams,  as  these  have  been  so  satisfactory  that 
no  one  would  think  of  going  back  to  the  old-fashioned  keyed  cam ; 
these  automatically  lock  themselves  into  position  according  to  a 
clip  on  the  cam-shaft.  The  position  of  this  clip  is  determined  by 
two  holes  bored  in  the  shaft  in  which  the  lugs  of  the  clip  are  set. 
By  drilling  two  extra  sets  of  holes  in  the  cam-shaft,  making  seven 
sets  to  a  battery  instead  of  the  usual  five,  it  will  be  possible  to 
change  from  one  order  of  drop  to  the  other.  Such  a  boring  would 
give  the  drops  1-3-5-2-4  and  3-1-5-2-4.  It  will  be  observed  that  the 
3-1-5-2-4  order  is  the  1-5-2-4-3  with  the  numbering  commencing  at 
the  third  stamp  to  enable  a  simpler  comparison  to  be  made  with 
the  other  order.  To  change  from  one  order  to  the  other,  it  would 
only  be  necessary  to  reset  the  first  two  cams  to  the  other  positions; 
a  thing  that  can  be  done  easily  and  quickly.  The  millman  now  has 
at  his  command  both  of  the  only  two  orders  of  drop  worthy  of 
consideration. 

Stem  Guide. — The  stem  guide  should  be  of  cast  or  malleable  iron 
and  of  the  individual  type,  though  wooden  guides  are  much  used 
in  the  older  mills.  They  should  be  bored  to  a  close  fit  of  1/32.io.  1/64 
in.  larger  in  diameter  than  the  stem,  carefully  aligned  and  adjusted 
when  first  run,  and  supplied  with  a  good  grade  of  lubricating  oil 
instead  of  the  usual  dirty  oil  or  scrap-grease.  They  should  be  kept 
as  tight  as  possible  without  heating  or  rubbing  so  that  the  stamp 
may  move  truly  up  and  down  with  little  side-play.  The  wooden 
guide  can  never  give  a  close  fit  without  heating,  and  sooner,  or 


GS 


CAM-STICK   AND   FINGER-JACK 


later  there  will  be  considerable  side-play  from  the  wearing  away 
of  the  wood;  they  are  not  being  placed  in  new  mills. 

Finger-Jack. — The  finger-jacks  should  raise  the  tappets  %  in. 
clear  of  the  cams,  so  that  a  cam-stick  of  three  and  not  to  exceed 
four  thicknesses  of  heavy  belting  may  be  used.  Thicker  cam- 


INDIVIDUAL   WOOD   GUIDES. 

(Stearns-Roger  Mfg.  Co.,  Denver.) 

sticks  are  too  heavy  to  handle  with  ease,  and  are  more  liable  to 
be  cut  to  pieces  by  a  stamp  with  too  long  a  drop.  One  very  thick 
cam-stick  should  be  kept  on  hand  to  increase  the  height  of  drop  of 
the  stamps  in  putting  in  shoes  or  stems  and  in  pounding  out  choked 
mortars.  A  box  3  by  6  in.  and  9  in.  deep,  and  open  at  the  top, 
should  be  fitted  to  the  central  battery-post  of  each  cam-shaft  for 
holding  the  cam-stick.  Cam-sticks  made  of  iron  with  handles  of 


I     •    I    •    I    •    I    • 


IDEAL  INDIVIDUAL   GUIDE. 

(Geo.  W.  Myers,  San  Francisco.) 


AUTOMATIC   FEEDER 


69 


leather  or  belting,  work  well,  but  care  must  be  used  in  placing 
them  on  the  cams  or  they  will  fly  back  in  a  dangerous  manner.  The 
finger-jacks  should  be  solid  and  steady ;  a  stamp  resting  on  a  wobbly 
finger-jack  a  fraction  of  an  inch  too  short,  and  in  connection  with 
loose  guides,  is  a  dangerous  thing  beneath  which  to  examine  the 
interior  of  a  mortar. 

Feeder. — The  suspended  type  of  the  Challenge  feeder,  or  one  of 
the  so-called  'improved'  feeders  of  the  same  order,  is  now  almost 
universally  used,  as  it  gives  a  free  floor  and  is  less  in  the  way  than 
the  platform  type.  However,  the  standard  platform  type  of  Chal- 
lenge feeder  is  still  the  strongest  and  most  satisfactory  working 


EUREKA    INDIVIDUAL    GUIDE. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 


machine  made.  The  revolving  feed-plate  should  be  set  4  in.  above 
the  mouth  of  the  mortar,  so  that  a  platform  of  wood  or  sheet-metal 
may  be  attached  to  the  mortar  to  catch  and  lead  into  the  mortar 
as  much  of  the  drippings  from  the  feeder  as  possible ;  and  also  to 
allow  of  the  introduction  of  a  long  tin  scoop  for  catching  a  sample 
of  the  mill-feed  as  it  drops  off  the  revolving  plate.  This  revolving 
feed-plate  should  be  provided  with  a  false  plate  or  liner  that  may 
be  readily  replaced  when  worn  out.  Feeders  were  formerly  actuated 


70 


AUTOMATIC    FEEDER 


by  a  bumper-rod  struck  by  a  cam  tappet,  but  as  these  rods  arc 
liable  to  give  trouble  at  times,  they  are  not  included  in  the  design 
of  a  modern  mill ;  a  small  'feed  tappet'  on  the  middle  stamp  striking 
the  arm  of  the  feeder  is  now  used.  This  tappet  should  be  a  split 


3      6 

£   o 


or  two-piece  collar,  since  in  changing  a  feed  stem,  putting  on  the 
feed  tappet  is  often  forgotten  until  after  the  stem  is  stuck  in  the 
boss.  These  tappets,  however,  frequently  give  trouble  by  slipping, 
due  to  grease  running  down  from  above,  or  to  the  bearing  parts 
being  too  smooth.  Feeders  are  the  only  parts  in  a  stamp-mill 


AUTOMATIC   FEEDER  71 

equipment  that  are  of  delicate  construction,  and  they  should  re- 
ceive careful  attention.  If  worn  out  or  broken,  they  should  be  re- 
newed or  rebuilt,  as  poor  feeders  cause  the  mill  employees  great 
annoyance,  and  reduce  the  mill  capacity  and  increase  the  breakages. 


FINGER-JACKS   OE   STAMP   FINGERS. 

(Denver  Engineering  Works  Co.,  Denver,  Colo.) 


STANDARD    SUSPENDED    TYPE    OF    CHALLENGE    ORE-FEEDER. 

Driven  by  feed  tappet  on  centre  stamp. 
(Traylor  Engineering  &  Manufacturing  Co.,  Allentown,  Pa.) 


72 


PERFORATED   SCREEN 


PLATFORM    TYPE    OF   CHALLENGE   FEEDER   WITH    BUMPER    ROD    FOR    DRIVING    BY    STAMP 

TAPPET. 

(Power  &  Mining  Machinery  Co.,  Cudahy,  Wis.) 

Screen. — Screens  for  use  in  stamp-milling  are  divided  into  two 
general  classes,  the  perforated  or  punched  metal  plate,  and  the 
woven  wire  or  'cloth'  screens.  Perforated  screens  are  either  plain 
or  burr-punched.  In  the  plain-punched  a  piece  of  the  metal  is 
punched  or  cut  out  to  make  the  hole,  while  in  the  burr-punched  the 
metal  is  bent  inward  instead  of  being  removed.  Burr-punched 
screens  require  to  be  placed  with  the  burr  or  ragged  edge  inside 
the  mortar  so  that  the  grains  of  pulp  may  not  wedge  in  the  orifices, 


TINNED-IRON    SCREEN  73 

and  thus  reduce  the  capacity  of  the  screen.  Even  the  plain- 
punched  screens  have  a  slight  burr  on  one  side  made  by  the  punch- 
ing tool  as  it  emerges  on  that  side  after  passing  through  the  plate ; 
it  is  generally  considered  that  this  burr  side  should  be  turned  inside 
the  mortar,  but  some  manufacturers  claim  the  reverse,  stating  that 
the  hole  becomes  slightly  larger  toward  the  burr  side  by  the  metal 
breaking  ahead  of  the  punching  tool.  These  plate  screens  are  gen- 
erally made  of  Russia  iron,  steel,  or  'tin  plate,'  though  sometimes 
of  brass,  copper,  bronze,  phosphor  bronze,  aluminum  bronze,  tin 
bronze,  aluminium,  zinc,  or  tin.  The  Russia  iron  screen  is  com- 
paratively thick  so  that  it  does  not  facilitate  discharge,  and  there- 
fore is  not  in  high  favor. 

The  'tin  plate'  or  'tinned-iron'  screen  is  made  of  a  good  grade 
of  iron  and  coated  with  tin.  This  coating  prevents  its  rusting  be- 
fore being  put  into  use,  and  may  prevent  an  acid  battery-water  or 
pulp  from  attacking  the  screen.  It  has  been  suggested  that  the 
coating  of  soft  tin  protects  the  screen  from  the  impact  and  attrition 
of  the  pulp  by  presenting  a  yielding  malleable  surface.  Some  mill- 
men  remove  the  coating  by  heating  the  screen  to  redness  over  a 
forge  or  gasoline  burner,  which  is  supposed  to  strengthen  the 
screen  by  annealing  it.  As  it  oxidizes  the  surface  of  the  screen, 
it  should  not  be  done  where  the  battery-water  or  pulp  is  acid.  Ex- 
periments can  easily  be  conducted  on  the  same  screen-frame  to  test 
the  value  of  annealing.  The  tinned-iron  screen  gives  the  least 
trouble  from  clogging.  This  is  because  of  the  thinness  of  the  metal. 
A  grain  of  quartz  that  will  lodge  in  a  hole  in  a  Russia  iron  or  thick 
steel-plate  screen,  will  pass  the  same  size  opening  in  a  tinned-iron 
screen,  or  will  be  jarred  through  by  the  moving  pulp  within.  The 
tinned-iron  screen  has  been  given  the  preference  in  many  mills 
after  being  tested  against  the  thicker  perforated  and  woven-wire 
screens.  The  character  of  the  rock  is  one  of  the  determining  factors 
in  the  choice  of  screen  to  be  used.  The  tendency  to  clog  with  a 
hard,  splintery  quartz  or  a  clayey,  talcose  ore  is  great,  and  it  is 
sometimes  possible  to  run  a  40-mesh  tinned-iron  screen  on  an  ore 
where  it  is  impossible  to  use  one  of  woven  wire  that  is  finer  than 
30-mesh  on  account  of  clogging. 

The  steel-plate  screen  is  the  strongest.  Its  life  is  so  long  that  it 
must  sometimes  be  removed  before  breaking  on  account  of  the 
openings  becoming  enlarged  by  wear.  Theoretically,  the  holes 
should  be  spaced  so  close  that  the  screen  will  break  when  the  holes 
have  become  enlarged  to  an  undesirable  extent.  Steel  screens  of 
special  thinness,  and  of  the  round-punched  type,  have  been  tried 


74  ROUND   VS.    SLOT-PUNCHED   SCREENS 

against  the  tinned-iron  with  satisfactory  results,  but  have  not  come 
into  the  general  use  they  merit. 

The  holes  in  punched  screens  are  of  two  kinds,  the  round  and 
the    slot.      The    slots    are    usually    half    an    inch    long    and    run 


SLOT-PUNCHED    PLATE    SCREEN.  ROUND-PUNCHED    PLATE    SCREEN. 

(Braun-Knecht-Heimann  Co.,  San  Francisco.) 

horizontally,  vertically,  or  diagonally.  The  diagonal  slot  is  given 
the  preference  over  the  vertical  for  no  particular  reason,  except  the 
theory  that  the  pulp  running  down  the  screen  must  sooner  come 
to  an  opening  and  by  running  along  the  opening  for  a  short  distance 
is  better  caused  to  pass  through  the  screen.  The  diagonal  and 
vertical  slot  have  been  found  superior  to  the  horizontal  slot>  for  it 
appears  that  to  get  the  best  results  the  length  of  the  slot  should 
run  in  the  same  general  direction  as  the  material  travels  over  the 
screen.  The  slot-punched  screen  gives  a  freer  discharge  and  greater 
capacity  with  less  blinding  than  the  round-punched  screen.  This 
is  partly  because  the  slot  screen  has  more  discharge  area  or  air 
space  and  partly  because  a  particle  of  ore  going  through  a  slot 
will  wedge  on  only  two  surfaces  and  will  have  a  chance  to  work 
itself  through  or  loose,  whereas  when  going  through  a  round  open- 
ing it  will  wedge  on  three  or  four  surfaces  and  have  more  friction 
to  overcome.  For  the  latter  reason  the  product  through  the  slot 
opening  will  be  more  inaccurately  sized  and  will  contain  many  flat 
pieces  of  pulp  that  could  not  possibly  get  through  a  round  opening. 
The  diagonal-slot  screen  is  advantageous  where  screens  blind  and 
clog  or  where  the  product  is  to  be  reground  and  the  uneven  sizing 
from  the  stamp  mortars  is  immaterial. 


DEFINITION  OF  'OPENING*  AND  'MESH3 


75 


A  plate  screen  is  numbered  the  same  as  the  number  of  the  sewing 
needle  that  will  just  pass  through  its  opening.  This  and  their 
method  of  manufacture  cause  them  to  be  spoken  of  as  needle-punched 
screens. 

SIZES  OF  ROUND  AND  SLOT-PUNCHED  PLATE  SCREENS 


Approximate  mesh  of 

Width  of  slot  or 

Width  of  slot  or 

Needle  number 

wire  cloth  to  which 

diameter  of  hole 

diameter  of  hole 

of  screen. 

openings  correspond. 

in  inches. 

in  millimeters. 

1 

12 

0.058 

L47 

2 

14 

0.049 

1.25 

3 

16 

0.042 

1.07 

4 

18 

0.035 

0.89 

5 

20 

0.029 

0.74 

6 

25 

0.027 

0.69 

7 

30 

0.024 

0.61 

8 

35 

0.022 

0.56 

9 

40 

0.020 

0.51 

10 

50 

0.018 

0.46 

11 

55 

0.0165 

0.42 

12 

60 

0.015 

0.38 

13 

70 

0.013 

0.33 

The  size  of  woven-wire  screens  is  designated  in  an  inexact  way 
by  their  'mesh'  and  in  a  scientifically  exact  way  by  their  'opening.' 


4-MESH,   0.105-INCH   WIRE   SCREEN. 

(W.  S.  Tyler  Co.,  Cleveland,  Ohio.) 

The  'mesh'  of  a  woven-wire  screen  is  the  number  of  openings  or 
air  spaces  per  lineal  or  running  inch,  and  is  determined  by  laying 
a  rule  upon  the  screen  and  counting  the  number  of  openings  em- 
braced within  the  length  of  one  inch.  As  screens  of  the  same 


76 


MESH   OF   WOVEN-WIRE   SCREENS 


number  of  meshes  are  made  from  various  diameters  of  wires,  it 
follows  that  the  size  of  the  openings  is  not  determined  by  the 
number  of  meshes  alone,  but  also  by  the  thickness  of  the  wire.  A 
30-mesh  screen  made  of  heavy  wire  will  have  a  larger  part  of  the 
screen  area  taken  up  by  the  wire  and  consequently  smaller  openings 
than  the  same  mesh  of  screen  when  made  of  lighter  wire.  The 
'opening'  or  'space'  between  the  wires  is  what  determines  the  size 
of  the  particles  passing  through  the  screen,  and  the  width  of  this 
opening  is  stated  in  inches  or  millimeters.  With  the  woven  slot 
screens  the  'opening'  is  the  width  the  narrow  way  and  has  no  re- 
lation to  the  length  of  the  slot.  The  size  to  which  the  product  must 
be  screened  determines  the  size  of  the  openings,  while  the  nature 
of  the  service  required  of  the  screen  determines  the  size  and  kind 
of  wires.  The  manufacturer  in  filling  an  order  requires  to  know 
the  opening,  the  shape  of  the  opening,  the  size  of  the  wire,  and  the 
kind  of  wire — unless  these  are  included  under  a  trade  number  of 
screen.  The  diameters  of  wires  have  been  stated  in  at  least  six 
different  'gauges,'  so  that  the  simplest  way  to  express  the  size  of 
wires  is  by  their  diameters  in  inches.  Thus  it  follows  that  the  only 
exact  way  to  describe  the  size  of  a  screen  is  to  give  its  'opening,' 
or  to  state  its  mesh  and  the  size  of  the  wire — which  will  allow  the 
'opening'  to  be  computed.  But  as  decimals  of  an  inch  do  not  quickly 
give  the  desired  impressions,  practical  millmen  speaking  in  a  gen- 
eral way  will  probably  continue  to  use  the  term  'mesh'  to  express 


STANDARD   TESTING    SCREEN. 

(W.  S.  Tyler  Co.,  Cleveland,  Ohio.) 


their  ideas  in  a  quickly  grasped  manner.  It  therefore  becomes 
necessary  to  standardize  in  some  arbitrary  manner  the  different 
meshes  by  considering  that  a  certain  opening  or  width  between 


STANDARD  SCREEN  SOALE  77 

wires  constitutes  a  certain  mesh,  irrespective  of  the  fact  that  with 
heavy  wires  there  will  be  less  than  the  stated  number  of  meshes 
per  lineal  inch,  or  with  light  wires  there  may  be  more  than  the 
stated  number.  This  is  possible  by  adopting  the  widths  of  open- 
ings used  in  the  Tyler  scale  or  series  of  standard  testing  screens' 
or  sieves.*  The  base  of  the  series  is  an  opening  of  0.0029  in.  which 
is  the  opening  in  200-mesh,  0.0021-in.  wire  cloth,  and  has  been 
standardized  by  the  U.  S.  Bureau  of  Standards.  The  width  of  the 
openings  in  each  sieve  increases  in  the  ratio  (as  originally  pro- 
posed by  Rittinger)  of  the  square  root  of  2,  or  1.414;  that  is,  the 
width  of  each  opening  in  any  screen  is  1.414  times  the  width  of 
the  openings  in  the  next  finer  sieve,  while  the  area  of  each  opening 
is  twice  as  large,  which  allows  spheres  or  grains  of  pulp  of  1.414 
times  the  diameter  or  twice  the  sectional  area  to  pass  through.  If 
the  openings  of  this  series  were  adopted  as  arbitrarily  designating 
these  meshes,  then  these  meshes  would  express  both  exact  and 
easily  grasped  ideas. 

TYLER  STANDARD  SCREEN  SCALE 

Ratio  V2~or  1.414  . 

Opening  Opening                                          Diam.  wire, 

in  in                                                dec.  of  an 

inches.             millimeters.  Mesh  inch. 

1.050  26.67  ..  0.149 

0.742  18.85  ..  0.135 

0.525  13.33  ..  0.105 

0.371  9.423  ..  0.092 

0.263  6.680  3  0.070 

0.185  4.699  4  0.065 

0.131  3.327  6  0.036 

0.093  2.362  8  0.032 

0.065  1.651  10  0.035 

0.046  1.168  14  0.025 

0.0328  0.833  20  0.0172 

0.0232  0.589  28  0.0125 

0.0164  0.417  35  0.0122 

0.0116  0.295  48  0.0092 

0.0082  0.208  65  0.0072 

0.0058  0.147  100  0.0042          ^ 

0.0041  0.104  150  0.0026 

0.0029  0.074  200  0.0021 

Woven-wire  screens  are  made  of  iron,  steel,  copper,  brass,  phos< 
phor  bronze,  and  aluminum  bronze.  They  are  of  two  kinds,  the 
single-crimp  and  the  double-crimp.  In  the  single-crimp  only  the 
wires  in  one  direction  are  crimped  or  bent,  and  the  result  is  that 

*Made  by  the  W.  S.  Tyler  Co.,  Cleveland,  Ohio. 


78  WOVEN-WIRE   SCREEN 

the  wires  of  such  screens  tend  to  spread  apart  and  make  the  open- 
ings of  irregular  size  and  produce  much  oversize  in  the  pulp.  In 
the  double-crimp  both  sets  of  wires  are  bent  and  arched  so  that 
they  are  locked  and  prevented  from  spreading.  The  woven-wire 
screens  are  made  with  square  openings  or  with  slot  openings, 
usually  horizontal  or  vertical. 


DOUBLE-CRIMPED    WIRE   CLOTH. 

(W.  S.  Tyler  Co.,  Cleveland,  Ohio.) 


The  Ton-Cap  (meaning  Tonnage-Capacity)  is  the  trade  name  of 
a  special  class  of  screen  made  by  a  prominent  manufacturer.*  To 
present  the  greatest  possible  discharging  area  or  screening  capacity 


f  c       ,     < 

iii  Mm 
ill  ii 


THE  TON-CAP   SCREEN. 

(W.  S.  Tyler  Co.,  Cleveland,  Ohio.) 


is  the  idea  along  which  it  is  designed.     It  is  double-crimped  and 
then  rolled,  which  sets  the  wires  and  keeps  them  from  slipping 
'Made  by  the  W.  S.  Tyler  Co.,  Cleveland,  Ohio. 


TON-CAP    SCREEN 


79 


out  of  place  or  spreading,  and  so  gives  an  even  product.  The 
rolling  also  presents  a  smoother  surface  which  is  more  easily  kept 
free  and  clean.  The  larger  area  in  the  woven-wire  screens  over 
the  plate  screens  is  further  increased  in  the  Ton-Cap  by  making 
the  openings  oblong  or  slotted.  In  this  way  it  has  the  largest  dis- 
charging area  of  any  screen,  and  therefore  is  a  highly  efficient 
screen  where  capacity  or  a  minimum  of  slime — as  for  concentrat- 
ing— is  desired.  These  screens  are  made  with  a  different  size  of 
wire  in  both  directions,  or  various  diameters  of  wires,  and  of  various 
lengths  of  slots.  This  results  in  several  hundred  kinds  of  screens, 
each  of  which  is  designated  by  a  trade  number.  In  this  way  the 
user  can  have  selected  for  him  a  screen  best  adapted  to  his  condi- 
tions. With  small  capacity  he  can  have  a  screen  of  fairly  heavy 
wire,  and  consequently  of  long  life.  He  can  use  a  screen  of  heavy 
wire  for  a  heavy  material  or  a  low  discharge,  or  one  of  light  wire 
for  a  light  material  or  a  high  discharge.  If  there  is  trouble  from 


Width  of  Slot,  0.027  Inch. 


Width  of  Slot,  0.027  Inch. 


0.367  Sq.  In. 
Discharge  Area  in 
1  Sq.  in. 


0.160  Sq.  In. 
Discharge  Area  in 
1  Sq.  in. 


No.  93  TOX-CAP 

0.367  sq.  in.  discharge  area  per  sq.  in. 
53.000  sq.  in.  discharge  area  per  sq.  ft. 


No.  6  DIAGONAL  SLOT  (25  mesh) 
0.160  sq.  in.  discharge  area  per  sq.  in. 
23.000  sq.  in.  discharge  area  per  sq.  ft. 


No.  93  Ton-Cap  has  129%  more  air  space  or  discharging  area  than  No. 
Diagonal  Slot  to  produce  the  same  sized  product. 

COMPARISON  OP  DISCHARGE  AREAS. 
(W.  S.  Tyler  Co.,  Cleveland,  Ohio.) 


blinding  or  choking  he  may  obtain  a  screen  having  longer  slots  or 
smaller  wires.  If  the  wires  in  one  direction  wear  out  more  rapidly 
than  in  the  other  direction,  he  can  secure  a  screen  in  which  the 
wires  are  selected  to  give  equal  life.  These  screens  are  usually 
made  in  steel  wire,  but  are  also  furnished  in  brass,  copper,  bronze, 
and  phosphor  bronze  wire.  They  are  a  high  development  in 


80  BRASS  SCREEN 

screens  and,  though  they  may  not  be  the  best  suited  screen  in  many 
cases,  they  should  be  thoroughly  tested,  especially  in  regard  to 
their  length  of  life  and  an  increase  in  tonnage  and  a  decrease  in  the 
percentage  of  slime  produced. 

Brass-wire  screens  have  been  found  satisfactory  for  fine  crushing 
with  a  high  discharge,  as  to  30  or  40-mesh  or  to  60-mesh — though 
crushing  in  a  stamp  mortar  through  a  60-mesh  screen  has  not  often 
been  performed.  Brass  wire  is  too  soft  for  the  severe  wear  and 
tear  of  crushing  with  a  low  discharge.  It  cannot  be  used  when 
crushing  in  cyanide  solution,  as  the  screen  is  attacked  by  the  so- 
lution, and  soon  breaks.  Contrary  to  the  usual  opinion,  they  do 
not  amalgamate  to  a  prohibitive  extent.  After  receiving  the  usual 
treatment  accorded  old  screens  for  removing  any  adhering  amalgam, 
they  can  be  melted  into  a  bar. 

The  brass,  copper,  or  bronze  screens — both  the  plate  and  woven 
cloth — are  used  where  the  battery  water  is  acid,  as  from  partly 
decomposed  sulphides,  and  iron  or  steel  screens  tend  to  rust  or 
corrode.  Bronze  screens  have  a  much  greater  life  than  iron  or 
steel  screens  and  it  would  often  be  advantageous  to  use  them,  even 
at  their  higher  cost. 

The  screen  to  be  used  can  only  be  determined  by  extended  experi- 
ments made  in  a  comparative  way  under  actual  working  conditions. 
Its  selection  is  influenced  by  the  following  factors  whose  weight 
or  influence  in  most  cases  is  not  fully  understood  or  clear:  Cost. 
Life.  Tonnage.  Effect  upon  extraction.  Nature  of  product. 
Accuracy  of  sizing.  Ability  to  screen  or  screening  capacity.  Dis- 
charging area.  Nature  of  ore.  Manner  in  which  screen  is  to  be 
used  and  service  required.  Type  of  screen  and  its  structurial 
features.  Thickness  of  plate  or  size  of  wire.  Size  and  shape  of 
opening.  Nature  of  screen  material.  Attention  required  by  screen. 
Trouble  from  clogging.  Loss  of  time  in  renewals.  Increase  in 
oversize  through  wear. 

The  ideal  screen  from  a  standpoint  of  screening  efficiency  would 
be  one  of  infinitely  small  wires  separating  the  openings.  On  the 
other  hand  the  ideal  screen  from  a  standpoint  of  service  would  be 
a  screen  with  infinitely  heavy  wires  between  the  openings.  How- 
ever, an  excess  of  screening  surface  and  discharge  area  is  not  of 
exceptional  advantage  in  stamp-mill  practice,  or  double-discharge 
mortars  would  be  used.  Likewise,  a  screen  of  heavy  plate  or  thick 
wire  is  not  of  advantage  even  with  an  excess  of  discharging  space, 
for  they  discharge  too  slowly  in  comparison  with  the  thin  plate  or 
woven  screens  of  light  wire,  and  as  a  result  a  heavy  wire  or  thick 
plate  screen  should  not  be  used  in  obtaining  a  fine  product. 


KIND   OF   SCREEN   REQUIRED  81 

The  thick  Russia-iron  screen  is  but  little  used  now.  For  crush- 
ing to  12  to  16-mesh  with  a  low  discharge,  the  diagonal-slot  steel 
screen  is  in  high  favor.  It  produces  an  inaccurately  sized  product 
having  large  angular  pieces  of  oversize,  but  such  crushing  is  usually 
followed  by  regrinding.  The  tendency  to  blind  or  choke  due  to  a 
hard,  splintery  ore  or  to  a  talcose  ore  is  at  a  minimum.  For  crush- 
ing between  16  and  30-mesh,  the  tinned-iron  screen  has  been  found 
very  satisfactory,  except  where  the  discharge  is  carried  too  low  to 
allow  these  screens  to  have  a  reasonable  length  of  life,  when  thin 
steel  screens  either  round-punched  or  with  diagonal  slots  may  be 
substituted.  It  is  questionable  if  these  16  to  30-mesh  screens  dis- 
charge sufficiently  fast  for  a  modern  fast-crushing  battery,  there- 
fore the  double-crimp,  rolled,  slot  type  of  woven-wire  screens — • 
the  Ton-Cap — should  be  tried. 

The  woven  wire  should  be  tested  against  the  plate  screens  in 
all  cases.  The  plate  screens  are  cheaper  and  usually  stronger,  but 
the  woven  wire  has  the  advantage  of  more  discharging  space,  which 
tends  to  produce  greater  capacity  and  less  slime.  Also,  the  round- 
ing surface  of  the  wires  seems  to  steer  the  particles  of  pulp  into  and 
through  the  opening,  but  on  the  other  hand  this  promotes  clogging. 
The  value  of  wire  screens  increases  as  their  tendency  to  clog  be- 
comes less.  The  clogging  tendency  is  overcome  by  using  the  slotted 
woven  type  and  by  using  smaller  wires  that  will  make  the  openings 
less  of  a  taper  in  which  the  grains  can  wedge.  If  clogging  still 
continues  the  plate  screens  should  be  tried,  and  particularity  those 
of  the  thinnest  metal  and  the  slotted  type.  Lime  in  the  crushing 
solution  sometimes  coats  wire  screens  so  that  punched  plate  must  be 
substituted. 

For  the  coarser  meshes  of  woven  wire  the  square  opening  will 
usually  answer  as  well  as  the  slot  opening.  The  round  openings  of 
the  punched  screens  will  give  the  most  accurate  sizing — provided 
the  screening  capacity  of  the  screen  is  in  excess  of  the  demands 
made  upon  it.  The  square  openings  of  the  woven  wire  will  give  the 
next  most  accurate  sizing,  but  a  slightly  coarser  product  than  from 
the  round  openings  of  the  same  width — because  of  the  difference 
in  shape  of  the  two  holes.  The  slot  openings  will  give  the.  most 
inaccurate  sizing  and  the  coarsest  product  for  the  same  width  of 
opening.  However,  the  above  statements  must  be  modified  by  the 
facts  that  the  plate  screens  have  the  smallest  discharge  area,  that 
the  square-opening  woven-wire  have  a  larger  discharge  area,  and 
that  the  slot-opening  woven-wire  have  the  largest  discharge  area; 
as  a  result  a  particle  of  pulp  splashed  against  a  punched  screen, 


82  CARE   OP   THE   SCREEN 

and  of  the  requisite  size  to  pass  through,  may  be  thrown  back  and 
recrushed  finer;  whereas  with  the  slot-opening  woven-wire  having 
a  much  larger  discharging  area  and  capacity,  there  is  a  much 
greater  tendency  for  the  particle  to  pass  through  the  screen  as  soon 
as  crushed  to  the  screen  size.  In  this  way  the  square  opening  and 
slotted  type  of  woven-wire  may  produce  more  accurate  sizing  than 
the  punched-plate  screens  by  reducing  the  amount  in  the  slime  and 
finer  sand. 

Accurate  sizing  and  long  life  do  not  go  together.  The  first  par- 
ticle of  ore  passing  through  an  opening  wears  the  wires  and  per- 
mits a  larger  piece  to  pass  through  the  next  time.  With  the  heavy 
wires  having  long  life,  the  openings  must  wear  very  coarse  and 
the  product  must  become  materially  changed — coarser — before  the 
screen  breaks.  With  the  light  wires,  the  openings  cannot  be  worn 
very  large  before  the  screen  breaks  and  must  be  replaced  with  a 
new  one.  Therefore  the  light  wire  screen  or  a  screen  of  thin  plate 
gives  the  most  accurate  sizing  at  the  expense  of  the  screen  life.  It 
is  generally  considered  that  the  openings  of  the  plate  screens  wear 
larger  much  more  rapidly  than  those  of  wire,  but  the  durability  of 
the  screen  material  is  what  really  determines  the  wear.  Screen 
tests  should  be  made  wet  on  the  pulp  issuing  from  new  and  from 
well-worn  screens  to  determine  if  the  openings  wear  larger  and 
thereby  deliver  an  appreciable  amount  of  over-size,  and  if  an  in- 
crease in  such  oversize  lessens  the  extraction  to  an  extent  warrant- 
ing the  removal  of  the  screen  before  it  is  fully  worn  out.  If  it  is 
found  advisable  to  remove  screens  for  this  reason,  a  laboratory  or 
small  testing  screen  of  such  a  mesh  that  it  will  retain  practically 
no  oversize  from  the  pulp  issuing  through  a  new  battery  screen 
should  be  used  in  the  mill,  and  when  the  pulp  from  any  battery 
screen  shows  an  undesirable  amount  of  oversize,  that  screen  should 
be  discarded.  If  the  discarded  screen  is  still  in  good  condition 
otherwise,  it  indicates  the  advisability  of  a  screen  of  thinner  plate 
or  smaller  wire,  or  with  the  holes  spaced  closer  together. 

When  screens  clog,  they  are  scraped,  brushed,  and  slapped  in  an 
effort  to  keep  them  clear.  Wire  screens  are  removed  when  badly 
clogged  and  left  to  become  dry,  when  they  are  brushed  and  slapped. 
Perforated  screens  usually  break  close  to  the  screen-frame.  In  such 
a  case  a  piece  of  wood  l1/^  in.  square,  and  slightly  longer  than  the 
break,  is  covered  with  canvas  or  a  piece  of  blanket  on  two  sides, 
and  attached  to  the  frame  by  one  or  two  short  nails  to  cover  the 
break  until  it  is  convenient  to  remove  or  turn  the  screen-frame.  The 
method  of  tacking  little  blocks  of  wood  or  rubber  belting  over 


CARE   OF   THE   SCREEN  83 

breaks  in  screens  is  followed  in  a  variety  of  ways,  and  is  one  of  the 
simple  expedients  by  which  the  cost  for  screens  is  kept  low. 

A  strip  of  canvas  or  gasket-rubber  between  the  screen  and  the 
frame  will  prolong  the  life  of  the  screen.  A  good  way  in  which  to 
attach  screens  to  the  frame  is  to  punch  them  over  a  template  to  fit 
small  bolts  in  the  screen-frame,  bolting  in  place  by  means  of  strap- 
iron,  using  a  hand  socket  wrench  for  the  nuts.  Strap-iron  at  the 
top  and  bottom  of  a  screen  is  a  good  protector.  Some  success  has 
been  attained  by  having  two  heights  of  screen-frames,  so  that  when 
the  screen  is  well  worn  at  the  top  and  bottom  through  turning  the 
screen-frame,  it  may  be  transferred  to  a  narrower  frame,  the  worn 
parts  now  coming  in  contact  with  the  frame. 

It  has  been  found  advisable  to  set  the  screen  in  the  mortar  at  an 
angle  from  the  vertical,  in  order  that  the  pulp,  besides  being  driven 
through  the  screen,  may  fall  on  it  and  run  through  as  it  flows  down 
after  the  splash.  An  angle  of  10  to  13°  from  the  vertical  has  been 
considered  sufficient. 


CHAPTER  IV 

WATER  SUPPLY — PRINCIPLES  OF  STAMP  CRUSHING — HEIGHT  AND 
SPEED  OF  DROP — WEIGHT  OF  STAMP — HEIGHT  OF  DISCHARGE — 
FEEDING  THE  MORTAR — POWER — INDIVIDUAL  STAMP. 

Water  Supply. — The  feed-water  for  a  battery  should  be  introduced 
into  the  top  or  into  the  feed-mouth  of  the  mortar,  using  a  pipe  on 
each  side  because  it  may  be  thought  necessary  to  introduce  more 
water  toward  one  end  of  the  battery  than  the  other,  though  this 
has  practically  no  effect  in  the  mortar.  The  valves  should  be 
accessible  from  the  front  of  the  mortar  for  the  convenience  of  the 


vj_ 


n 


p/v> 


ARRANGEMENT   OF   PIPING   ON    10-STAMP   BATTERY. 

(Denver  Engineering  Works  Co.,  Denver,  Colo.) 


millman,  and  there  should  be  two  to  each  pipe;  one  being  a  gate- 
valve — a  globe-valve  cannot  be  so  easily  cleaned  of  trash — by  which 
the  exact  quantity  of  water  used  is  regulated,  and  the  other  a  bibb 
or  plug  cock.  When  it  is  necessary  to  shut  off  the  feed-water,  the 
plug  cock  is  used,  and  when  starting  again,  it  is  thrown  wide  open. 
Thus  no  time  is  lost  in  adjusting  the  amount  of  water,  as  that  is 
provided  for  by  the  gate-valve.  The  water-supply  should  come 
from  a  tank  having  a  constant  head,  for  there  should  be  no  varia- 

84 


WATER-SUPPLY    PIPING  85 

tion  in  the  amount  of  water  flowing  over  the  plates.  Where  the 
water  is  returned  for  re-use  or  is  received  in  a  storage  tank,  this 
tank  should  have  large  area  in  order  to  avoid  a  rapid  reduction  in 
the  head.  The  main  water-supply  pipes  entering  the  mill  and  run- 
ning the  length  of  the  batteries  should  be  of  large  diameter  so  that 
the  amount  of  water  passing  into  one  mortar  may  not  be  decreased 
or  increased  by  starting  or  stopping  the  flow  into  the  other  mortars. 

When  crushing  in  cyanide  solution  the  pipes  become  gradually 
encrusted  or  lined  with  salts  of  lime  from  that  added  in  the  cyanide 
plant  and  of  alumina  from  the  clay  constituents  of  the  ore.  Such 
pipes  should  be  large  in  diameter,  and  have  tees  instead  of  elbows, 
and  many  unions,  to  enable  them  to  be  easily  taken  part  and  cleaned. 
Launders  have  been  used  instead  of  pipes  to  avoid  this  trouble. 

Attempts  have  been  made  to  introduce  the  water  in  the  front  or 
rear  of  the  mortars  and  on  a  level  with  or  just  below  the  tops  of  the 
dies.  The  arguments  advanced  are  that  the  finer  material  is  thus 
floated  up  and  out  of  the  mortar,  and  that  the  pulp  just  below  the 
face  of  the  die  is  kept  active,  permitting  the  amalgam  to  sink  into 
it  and  be  caught.  It  would  require  a  higher  head  of  water  than  can 
ordinarily  be  obtained,  and  in  fact  higher  than  it  is  desirable  to 
use,  to  overcome  the  violent  pulsations  imparted  to  the  pulp  by  the 
falling  stamps  and  to  give  a  classifying  effect  in  the  mortar;  and 
should  it  overcome  these  pulsations,  the  result  would  be  to  interfere 
with  the  even  distribution  of  the  pulp  over  the  dies.  On  account 
of  the  wearing  of  the  dies,  it  is  impossible  for  the  feed-water  to  enter 
at  the  proper  point  in  relation  to  the  face  of  the  dies  for  any  great 
length  of  time.  Where  the  water  has  been  introduced  in  the  rear 
of  the  mortar,  it  has  been  found  that  when  the  dies  are  nearly  worn 
out  and  the  screen  is  consequently  set  low,  the  water  shoots  across 
the  mortar  and  through  the  screen.  Furthermore,  it  is  almost  im- 
possible to  maintain  a  water-tight  connection  between  a  pipe  and  a 
mortar. 

Should  the  feed-water  be  shut  off  without  warning,  the  stamps 
must  be  hung  up  with  all  possible  speed,  for  they  will  sink  down 
through  the  pulp  to  the  die  and  continue  falling  and  feeding  ore 
until  the  mortar  is  choked  with  ore  and  pulp.  Owing  to  the  absence 
of  water,  the  pulp  does  not  run  or  splash  back  under  each  stamp. 

The  amount  of  feed-water  used  in  a  mortar  is  gauged  by  the  flow 
of  the  pulp  over  the  plates,  the  water  being  used  in  such  quantities 
as  to  give  ideal  conditions  for  amalgamating  on  the  plate-tables, 
rather  than  to  supply  the  quantity  that  will  give  the  greatest  crush- 
ing and  screening  effect  in  the  mortar.  The  amount  of  water  used 


86  CRUSHING   BY   IMPACT 

per  ton  of  ore  stamped  varies  from  4  to  10  tons.  Where  effective 
amalgamation  takes  place  on  a  short  apron-plate,  Ql/2  tons  will  be 
about  the  average  amount.  The  crushing  capacity  of  a  battery  in- 
creases with  the  amount  of  water  used,  up  to  the  point  where  a 
good  splash  or  wave  motion  on  the  screen  can  no  longer  be  secured. 
This  increase  in  capacity  is  more  noticeable  in  a  mortar  with  a  deep 
discharge  than  with  a  shallow  one,  for  such  a  mortar  sizes  and  dis- 
charges hydraulically  to  a  much  greater  extent  than  one  with  a 
low  discharge.  If  large  quantities  of  water  are  used  the  amalgama- 
tion is  usually  not  so  effective,  long  outside  plates  and  auxiliary 
amalgamating  devices  then  being  required  for  the  purpose  of  get- 
ting a  good  contact  between  the  pulp  and  the  amalgamated  surface. 

Principles  of  Stamp  Crushing. — The  stamp  battery  crushes  in 
two  ways,  by  compression  as  the  result  of  the  impact  of  the  stamp 
falling  upon  the  ore  over  the  die,  and  by  the  abrasion  or  attrition 
of  the  particles  of  rock  upon  each  other  when  moving  from  the 
impact  of  the  stamp.  Crushing  by  impact  is  especially  the  case  with 
coarse  ore,  but  it  is  not  necessary  that  each  piece  and  particle  of  rock 
be  caught  between  the  metal  surfaces  of  the  shoe  and  die,  nor  is 
the  crushing  by  impact  confined  to  the  coarse  rock.  The  strains  of 
compression  from  the  impact  are  communicated  to  all  the  coarse  ore 
in  the  bed  between  the  shoe  and  die.  This  strain  is  also  communi- 
cated to  the  finer  particles  of  ore  caught  fairly  between  the  larger 
pieces.  The  coarse  ore  in  responding  to  the  compressive  strain  and 
moving  from  and  adjusting  itself  to  the  compression  of  the  stamp, 
produces  an  abrasive  effect  in  all  directions,  which  is  one  of  the 
principal  means  by  which  the  finer  particles  are  still  further  reduced. 
The  reduction  of  the  finer  particles  by  abrasion  under  the  stamp 
must  be  very  similar  to  that  which  takes  place  in  the  tube-mill.  A 
consideration  of  these  principles  will  show  wherein  stamp-mill 
crushing  is  radically  different  from  all  other  forms  of  rock-reduction, 
will  point  out. why  the  limit  of  economy  can  be  passed  in  fine 
breaking  in  the  rock-breaker,  and  will  indicate  why  a  fine  or  a  soft 
talcose  ore  often  requires  the  addition  of  coarse  or  hard  ore  to  act 
as  the  'grinders'  before  it  can  be  satisfactorily  crushed  or  com- 
minuted. 

The  most  effective  method  of  crushing  is  by  impact,  but  as  a 
particle  of  ore  becomes  finer  it  becomes  increasingly  harder  to 
catch  it  fairly  between  two  surfaces  so  that  it  may  be  further 
crushed  or  comminuted.  It  is  largely  because  of  this  that  very  fine 
crushing  becomes  difficult  in  the  stamp  battery.  It  is  now  recognized 
that  the  tube-mill  crushes  mainly  by  the  impact  of  the  falling  peb- 


SIZE   OF   ROCK   FOR   STAMPING  87 

bles,  rather  than  through  abrasion  similar  to  that  of  the  grinding 
mill ;  and  that  the  pebbles  of  the  charge  should  be  large  enough  and 
the  grains  of  pulp  small  enough  that  the  ore  particles  are  shattered 
by  the  falling  pebbles;  also  that  intermediate  sizes  of  pebbles  or 
pulp  are  detrimental.  Time  may  show  that  the  principles  of  stamp- 
ing and  tube-milling  are  the  same  to  a  much  greater  extent  than  is 
now  realized. 

Much  has  been  said  in  regard  to  step  or  stage  reduction — the  re- 
moval of  the  ore,  as  soon  as  it  has  been  reduced  to  a  certain  size,  to 
another  machine  which  will  make  a  further  reduction  and  pass  it  on 
to  another  machine  which  will  make  a  still  further  reduction.  This 
is  more  a  beautiful  theory  than  a  practical  reality  applicable  to 
low-cost  milling,  for  no  economically  successful  and  satisfactory 
method  of  separating  or  screening  the  ore  when  it  has  been  re- 
duced to  the  proper  sizes  has  yet  been  devised.  The  stamp-mill  has, 
within  certain  limitations,  the  happy  faculty  of  being  able  to  crush 
both  fine  and  coarse  ore  at  one  operation  with  reasonable  efficiency 
on  both,  and  herein  is  one  of  the  features  by  which  the  stamp-mill 
retains  its  supremacy.  The  work  of  the  stamp-mill  would  not  be 
more  satisfactory  in  crushing  coarse  ore  if  the  medium-size  ore  or 
pulp  was  removed  as  fast  as  made.  And  it  would  not  satisfactorily 
recrush  coarse  tailing  unless  some  coarse  rock  was  fed  with  the 
tailing. 

Height  and  Speed  of  Drop. — The  height  of  drop  to  be  given  the 
stamps  depends  on  the  size  and  hardness  of  the  ore,  on  the  weight 
of  the  stamps,  and  to  some  extent  on  the  treatment  required  for 
the  ore.  Hard  ore  will  require  a  heavier  blow  and  consequently  a 
longer  drop  than  soft  ore.  Similarly  a  small  piece  of  ore  will  not  re- 
quire as  hard  a  blow  or  as  long  a  drop  as  when  coarse.  Consequently 
a  hard,  tough  ore  should  be  broken  finer  in  the  breaker  than  soft, 
brittle,  friable  material.  It  would  appear  that  the  size  to  which  the 
ore  should  be  broken  in  the  breaker  would  have  some  relation  to 
the  thickness  of  the  bed  of  pulp  between  the  shoe  and  die,  but  in 
actual  practice  the  softness  and  nature  of  the  ore  is  the  determining 
factor.  Millmen  prefer  to  have  the  ore  broken  to  what  niay  be 
termed  'a  medium  coarse  size,'  rather  than  pulverized  fine,  as  such 
ore  feeds  better  and  causes  the  battery  to  work  more  evenly.  Also, 
as  just  noted,  some  ores  that  are  soft  or  brittle  rather  than  hard, 
tough,  and  close  grained,  appear  to  crush  faster  when  containing 
coarse  material  which  increases  the  attrition.  This  point  should  be 
investigated  in  determining  the  proper  size  for  preliminary  crush- 
ing in  the  breaker.  To  crush  a  hard  rock  to  a  size  approximating 


88  DROP   AND   SPEED   OF   STAMP 

%  in.  diam.,  and  a  soft  rock  to  iy2  in.  would  appear  ideal,  but  in 
practice  it  is  all  crushed  to  a  maximum  diameter  of  1%  to  2l/2  inches. 

For  a  hard  ore  a  drop  of  7  to  10  in.  is  usual,  for  a  medium  ore 
from  6  to  8  in.,  and  for  a  soft  ore  from  4^>  to  G1/^  in.  Increasing  the 
weight  of  the  stamps,  and  breaking  the  rock  finer  in  the  breaker 
permits  a  shorter  drop  to  be  used.  As  the  height  of  drop  is  lessened, 
the  stamps  should  be  run  faster  on  the  principle  that  they  should 
drop  as  fast  as  possible ;  the  increased  speed  thus  partly  offsets  the 
loss  of  crushing  power  through  shortening  the  length  of  drop. 
Theoretically,  a  short  drop  and  higher  speed  indirectly  increase  the 
capacity  by  keeping  the  finer  material  in  better  suspension  and  by 
washing  it  out  of  the  mortar  faster ;  and,  consequently,  is  the  better 
method  where  concentration  is  practiced  or  it  is  desired  to  produce 
a  minimum  of  slime.  Too  short  a  drop  at  the  maximum  speed  may 
not  allow  the  die  to  become  covered  with  pulp.  The  speed  at  which 
stamps  can  be  run  safely  has  been  worked  out  mathematically,  but 
the  millman  desirous  of  maintaining  a  high  tonnage  will  run  the 
stamps  as  fast  as  possible  up  to  the  point  where  the  tappet  just 
stops  short  of  falling  on  the  cam  when  the  stamp  is  at  its  maximum 
height  of  drop.  An  increase  of  %  in.  in  the  drop,  without  de- 
creasing the  speed,  is  often  possible  by  careful  work  where  the  run- 
ning speed  does  not  vary.  An  increase  in  this  way  from  a  7y2-in.  drop 
to  an  8-in.  drop  will  increase  the  crushing  capacity  by  6%  per  cent. 

The  maximum  speed  possible  and  being  used  is  about  115  drops 
per  minute  at  6  in.,  108  drops  at  7  in.,  100  drops  at  8  to  Sl/2  in.,  and 
90  drops  at  10  to  lO1/^  in.  Instances  have  been  reported  where  the 
speed  has  been  decreased  from  the  maximum  limit  without  decreas- 
ing the  tonnage  crushed.  This  was  undoubtedly  due  to  a  bad  order 
of  drop  or  such  poor  action  within  the  mortar  that  the  pulp  was 
not  bedded  as  evenly  over  the  die  or  so  well  splashed  over  the 
screen,  especially  the  first,  when  using  the  maximum  number  of 
drops.  On  an  average  ore  a  6  to  6i/2-m-  drop  is  the  usual  practice 
where  concentration  is  used,  whether  for  the  reason  cited  in  the 
preceding  paragraph  or  from  custom  is  not  apparent.  The  usual 
practice  upon  the  same  ore  where  concentration  is  not  used,  is  a 
7y2  to  9-in.  drop. 

The  power  required  by  a  stamp  increases  directly  with  the  height 
of  drop,  or,  to  be  more  exact,  with  the  height  through  which  it  is 
lifted.  This  is  expressed  by  multiplying  the  weight  of  the  stamp 
in  pounds  by  the  distance  in  feet  through  which  it  is  raised,  and 
calling  the  result  foot-pounds.  This  power  has  been  spent  in  over- 
coming the  resistance  of  gravity  and  represents  that  much  potential 


INCREASED   TONNAGE   OP    HIGHER   DROP  89 

energy  stored  in  the  stamp.  When  the  stamp  falls  the  same  height, 
this  amount  of  energy  must  be  expended  against  some  resistance 
before  the  stamp  will  come  to  a  rest  or  in  the  impact  of  the  shoe 
upon  the  ore  and  die  and  mortar  beneath,  less  the  friction  of  the 
guides  and  the  atmosphere — which  will  be  neglected  herein.  If  a 
stamp  weighing  1000  Ib.  was  allowed  to  fall  freely  through  a  dis- 
tance of  one  foot  upon  a  perfect  mechanism  and  there  was  no 
friction,  the  power  utilized  in  lifting  the  stamp  would  be  so  restored 
that  another  1000-lb.  stamp  could  be  lifted  1  ft.,  or  a  100-lb.  stamp 
lifted  10  ft.  This  is  in  accordance  with  the  well  known  physical 
law  of  conservation  of  energy  and  the  experience  with  pile  drivers. 
Therefore  the  crushing  power  of  a  stamp  increases  directly  with  the 
height  to  which  the  stamp  is  lifted  and  through  which  it  drops,  just 
'as  the  power  does  which  is  required  to  operate  the  stamp.  The 
erroneous  statement  has  been  repeatedly  made  that  the  crushing 
force  of  a  stamp  varies  as  the  square  root  of  the  height  through 
which  it  falls,  and  that  the  most  economical  way  of  employing 
power  in  a  stamp-mill  is  by  making  the  weight  of  the  stamp  as  great 
and  the  height  of  drop  as  small  as  is  convenient.  The  following 
table  has  been  prepared  by  using  the  common  heights  of  drop  at 
their  highest  speeds  in  practice : 


ft 

05 

bO 

W) 

05      £< 

CO 

.3 

2 

af 

a 

a 

o?  ~    a 

1 

2 

HJ 

"S 

3 

CO 

JB 

C/3 

"S     ^     ° 

a 

£H 

CO 

05 

13 

O>          ^ 

ft 

fi 

I*     O> 

«    ft 

O    £3 

2    o  ^3 

a 

2 

ft 

1 

M 

s  a 

8  C  d 

ft  £    cS 

2 

• 

05     o< 

'3        tH 

'3  i-i 

05           t^ 

<M 
O 

>d 

0    £ 

'"S     * 

*  s 

*  a 

1st 

1 
1 

Numbei 

|rH 

|  .2 

la 

o 

11 

|1 

*-"    £1     m 
|ll 

O 

6 

115 

690 

100.00 

1.0000 

115.00 

100.00 

7 

108 

756 

109.57 

1.1667 

126.00 

109.57 

8% 

100 

850 

123.19 

1.4167 

141.67 

123.19 

10% 

90 

945 

136.96 

1.7500 

157.50 

136.96 

A  consideration  of  this  table  indicates  that  the  power  required 
grows  greater  very  rapidly  as  the  height  of  drop  at  its  maximum 
speed  is  increased,  and  that  the  crushing  force  increases  at  the  same 
rate.  It  shows  that  the  maximum  crushing  is  effected  by  a  stamp 
when  using  a  high  drop,  for  with  a  short  drop  the  stamp  is  at  rest  or 
at  less  than  the  maximum  speed  for  a  greater  proportion  of  the  time. 
The  table  also  shows  that  the  heavier  stamps  with  a  shorter  drop 
have  no  greater  efficiency  than  a  lighter  stamp  with  a  higher  drop. 


90  EFFECT  OF  VELOCITY  OF  STAMP 

To  illustrate  from  the  above  table  and'  the  knowledge  that  the  crush- 
ing force  of  a  stamp  is  the  'height  of  drop'  X  'speed  of  drop'  X 
'weight  of  stamp,'  a  1000-lb.  stamp  with  a  lOVij-m.  drop  may  be 
assumed  to  give  a  crushing  force  of  136.96  units.  If  a  6-in.  drop 
was  used  at  its  maximum  speed  it  would  require  a  stamp  of  1369.6 
Ib.  weight  to  give  the  same  crushing  effect,  but  the  power  to  operate 
would  remain  the  same. 

There  is  another  advantage  in  the  use  of  the  high  drop.  An  object 
or  a  stamp  falling  freely  increases  its  velocity  or  speed  of  falling 
with  the  square  root  of  the  distance  through  which  it  falls.  As  the 
height  of  drop  is  increased  the  stamp  will  impinge  upon  the  ore  at 
a  higher  speed  and — disregarding  the  heavier  weight  of  the  blow — 
will  strike  a  quicker,  sharper  blow.  Ore  tends  to  deform  and  be- 
come elastic  and  plastic,  instead  of  rupturing  and  fracturing,  to  a 
much  greater  extent  when  struck  slowly  than  when  struck  with  a 
high  velocity.  This  is  clearly  indicated  by  the  results  of  swift  blows 
of  light  hammers  as  against  slow  blows  of  heavy  hammers  in  break- 
ing rock,  or  in  the  running  of  crushing  rolls  at  slow  and  at  high 
speeds.  A  1000-lb.  stamp  falling  12  in.  should  have  the  same  energy 
and  the  power  to  crush  the  same  amount  of  ore  as  a  2000-lb.  stamp 
falling  6  inches,  but  because  of  its  greater  velocity  due  to  its  higher 
fall  should  be  better  able  to  fracture  and  crush  the  ore.  The  extent 
to  which  the  length  of  drop  can  be  increased  to  secure  these  ad- 
vantages is  limited  by  what  is  convenient  and  desirable  in  a  me- 
chanical way,  for  as  the  height  of  drop  is  increased  a  point  is  soon 
reached  where  the  stamp  becomes  difficult  to  handle  and  breakages 
commence  to  occur. 

Weight  of  Stamp. — In  the  earlier  mills  the  stamps  weighed  from 
500  to  750  Ib. ;  this  has  been  increased  until  in  America  the  weight 
of  a  standard  stamp  with  a  new  shoe  is  1000  Ib.,  with  a  tendency 
to  increase  to  1250  Ib.  Extended  experiments  made  in  the  past  in 
some  large  mills  indicated  1000  Ib.  to  be  the  best  weight  in  the 
judgment  of  the  experimentors.  The  reason  given  was  that  a 
heavier  stamp  crushed  more  ore  than  the  plates  could  handle.  In 
South  Africa  the  tonnage  has  increased  with  the  weight  of  the 
stamps,  the  favorite  weight  now  being  1750  to  2000  Ib.,  and  in  one 
case  2200-lb.  stamps  have  been  installed.  Attempts  have  been  made 
to  show  theoretically  that  this  is  passing  beyond  the  economic  weight 
for  a  stamp,  and  it  may  mark  the  maximum  weight  of  the  gravity 
stamp ;  yet  much  heavier  gravity  stamps  may  be  tried  in  imitation 
of  the  steam  stamp  which  is  an  effective  crusher  and  strikes  a  much 
more  powerful  blow  than  any  gravity  stamp  now  in  use.  Capacities 


91 


THE    JOSHUA    HENDY    HEAVY    STAMP    OF    THE    1500    TO    2000-LB.    TYPE. 


92 


INCREASING    WEIGHT   OF   STAMP 


higher  than  10  tons  and  up  to  20  tons,  and  even  more  with  ex- 
tremely coarse  crushing,  have  been  attained  with  these  heavier 
stamps. 

DIMENSIONS  AND  WEIGHTS  OF  STAMP-BATTERY  PARTS 


850 


1000 


Weight  of  Stamp,  Ib. 
1050   1250   1500 


1600        1800 


Shoe,  weight,  Ib  

>  .  .  . 

v>2  **.v 

150 

170 

170 

200 

242 

242 

242 

Die,  diam.  of  body,  in. 

81 

9i 

9i 

9i 

H 

9i 

9i 

Die,  6  in.  high,  weight, 

Ib. 

106 

122 

122 

122 

122 

122 

122 

Die,  7  in.  high,  weight, 

Ib. 

121 

140 

140 

140 

140 

140 

140 

Die,  8  in.  high,  weight, 

Ib. 

136 

157 

157 

157 

157 

157 

157 

Bosshead,  diam.  by  height, 

in 

84x18 

9x18 

9x19 

9ix22 

9|x264. 

9}x304. 

9Jx37 

Bosshead,   weight,    Ib.. 

232 

270 

285 

350 

420 

498 

621 

Tappet,   3   keys,   diam. 

by 

height,  in  

9x12 

9Jxl4 

9£xl4 

9^x15 

94x15 

94x15 

94x17 

Tappet   weight   Ib 

136 

155 

155 

170 

185 

185 

212 

Cam,  diam.  of  hub,  in. 

12 

12 

12 

134 

14 

14 

14 

Cam,  weight,  not  less  than, 

Ib  

180 

200 

200 

225 

235 

235 

240 

Stem,  diam.  by  length, 

in.3ix!68 

3§xl68 

3^x168 

3fxl74 

4x186 

4x192 

4x234 

Stem,  weight,  Ib  

365 

426 

455 

545 

661 

683 

725 

Cam-shaft,    diam.    (length 

144.  ft),  in  

5i 

5i 

6 

7 

7 

7J 

7i 

Cam-shaft,   weight,    Ib. 

1120 

1280 

1400 

1915 

1915 

2050 

2050 

Cam-shaft  Pulley,  diam.  by 

face,  in  

72x14 

78x16 

84x16 

84x18 

84x20 

84x22 

84x24 

(Denver 

Engineering  Works  Co., 

Denver, 

Colo.) 

The  weights  of  the  different  parts  of  a  1000-lb.  stamp  are  approxi- 
mately :  stem,  43%  ;  tappet,  15;  boss,  26;  shoe,  16.  The  weight  of  a 
stamp  may  be  increased  in  two  ways,  by  placing  an  extra  tappet 
on  the  stem,  either  above  or  below  the  upper  guide,  or  by  using  a 
false-shoe;  this  shoe  is  identical  with  the  regular  shoe  used,  with 
the  exception  that  it  has  a  socket  similar  to  the  shoe-socket  of  the 
boss.  The  false-shoe  is  first  put  on  in  the  usual  way  after  which 
the  regular  crushing  shoe  is  put  on.  A  variation  of  the  plan  of 
using  an  extra  tappet  is  to  clamp  to  the  stem  at  any  convenient 
point  one  or  more  heavy  metal  collars  or  discs  similar  to  the  two- 
piece  collars  used  on  cam-shafts.  Placing  weights  high  up  on  the 
stem  has  not  been  found  entirely  satisfactory,  as  the  center  of 
gravity  of  the  stem  is  raised  higher  up,  making  the  stem  'top-heavy' 
and  thereby  causing  more  wrenching  of  it  and  greater  wear  on  the 
guides  and  more  broken  stems.  The  use  of  false  shoes  or  the  placing 


93 


TWO-STAMP    MILL    MUCH    USED   BY    PROSPECTORS. 

(Union  Iron  Works  Co.,  San  Francisco.) 


94  INCREASING   WEIGHT   OF   STAMP 

of  the  tappets  or  collars  on  the  lower  end  of  the  stem  at  the  boss  is 
good.  With  the  exceptionally  heavy  stamps  now  being  used  in 
some  mills,  the  extra  weight  is  obtained  mainly  and  almost  wholly 
in  some  cases  by  increasing  the  length  of  the  boss  which  is  allowed  to 
project  up  through  the  top  of  the  mortar ;  this  is  good  practice.  It 
has  been  impossible  to  get  millmen  to  take  an  interest  in  any  of  these 
ways  of  increasing  the  weight  of  a  stamp  when  the  shoe  is  worn 
down,  though  the  decrease  in  capacity  is  readily  noticeable,  especi- 
ally with  the  lighter  stamps,  the  shoes  of  which  have  sometimes 
been  removed  before  being  worn  down,  solely  to  get  the  increased 
capacity  due  to  the  greater  weight  of  newly-shod  stamps. 

WEIGHT  OF  STAMP  PARTS 

(Subject  to  much  variation) 

Stem.  Tappet..  Bosshead.  Shoe.  Total. 

380  110                 215                 145                   850 

380  120                 255                 145                   900 

395  135                 252                 168                   950 

435  145                 262                 158  1000 

444  169                 252                 185  1050 

492  168                 305                 185  1150 

575  135                 364                 176  1250 

604  135                 276                 235  1250* 

604  135                 442                 269  1450* 

706  250                 408                 286  1650* 

692  232                 788""                288  2000* 

556  282                 872                 290  2000* 
*South  Africa. 

What  determines  the  weight  of  stamp  to  be  used?  Properly,  the 
hardness  of  the  ore  and  the  tonnage  desired,  but  ordinarily,  custom. 
That  custom  regulates  the  weight  is  proved  by  the  fact  that  though 
it  has  been  fully  demonstrated  that  the  tonnage  increases  with  the 
weight  of  the  stamps,  but  little  attempt  has  been  made  in  America 
to  increase  their  weight  in  the  many  installations  made  in  the  past 
where  amalgamation  is  not  practised.  Most  of  these  stamps  have 
weighed  1000  lb.,  some  1250,  and  a  very  few  1500.  Even  if  amal- 
gamation is  to  be  practised,  heavy  stamps  should  be  employed,  as 
some  system  of  handling  the  pulp  can  always  be  devised.  A  study 
of  the  results  of  comparative  trials  of  stamps  of  different  weights 
and  of  the  general  results  from  heavy  stamps  in  comparison  with 
light  stamps,  indicates  that  the  tonnage  crushed  increases  directly 
with  the  weight ;  that  is,  if  a  1000-lb.  stamp  will  crush  four  tons 
per  day,  a  1250-lb.  stamp  will  crush  approximately  five  tons,  and  a 
1500-lb.  stamp  will  crush  six  tons. 


AMALGAMATING   TABLES   FOR    HEAVY   STAMPS 


-  95 


Heavy  stamps  cost  more  to  install  as  all  parts  must  be  correspond- 
ingly heavier,  they  also  require  more  power,  but  do  not  appear  to 
require  much  more  labor,  and,  taken  as  a  whole,  their  increased 
capacity  tremendously  outweighs  their  extra  cost. 

A  stamp  lighter  than  1000  Ib.  should  not  be  ordered,  even  for  a 
soft  ore,  for  should  the  stamp  break  through  the  bed  of  the  pulp 
and  strike  the  die,  a  shorter  drop  can  be  used.  The  heavy  stamp 
is  well  adapted  for  coarse  crushing,  and  with  the  increasing  use  of 


FALSE    SHOE    AND   COLLAR   FOR   INCREASING   WEIGHT   OF    STAMP. 


tube-mills  for  fine  grinding  it  may  be  expected  that  heavier  stamps 
will  be  used.  There  is  no  reason  why  the  modern  stamp-mill  in 
America  should  not  be  equipped  with  1500-lb.  or  1750-lb.  stamps, 
and  arrangements  made  to  divide  the  pulp  between  two  amalgamat- 
ing tables  placed  one  in  front  of  the  other. 

This  can  be  accomplished  by  bolting  to  the  mortar  a  distributing 
box  having  as  many  as  sixteen  holes.  The  pulp  passes  from  the 
mortar  across  the  extra  wide  lip  plate,  and  in  equal  amount  and  a 
homogenous  condition  through  each  of  these  holes.  Attach  an 
auxiliary  distributing,  or  rather  catching  box,  that  will  catch  the 
flow  of  eight  alternate  holes,  leaving  the  flow  from  the  other  eight 
holes  to  pass  over  the  plate  in  front  of  the  mortar.  Have  the  catch- 
ing box  empty  its  flow  into  a  pipe  or  launder  at  the  side  and  head 


96 


INFLUENCE   OF   DISCHARGE    HEIGHT  97 

of  the  table  in  front  of  the  mortar.  By  this  pipe  or  launder  lead 
the  flow  to  a  table  set  in  front  of  the  first  table  and  on  a  slightly 
lower  bench  of  the  mill.  This  method  will  give  the  thin  flow  of 
dilute  pulp  that  is  essential  to  good  amalgamation. 

The  capacity  of  a  first-class  modern  1000-lb.  stamp-battery  in 
America  can  be  estimated  at  4  tons  per  24  hours  through  a  30-mesh 
screen.  There  are  so  many  varying  factors  that  the  tonnage  ranges 
from  3  to  6  tons,  but  4  will  be  found  the  average  capacity. 

Height  of  Discharge.— The  height  of  discharge  to  be  used  depends 
upon  whether  coarse  or  fine  crushing  is  to  be  done ;  whether  or  not 
an  attempt  is  made  to  catch  much  of  the  gold  in  the  mortar ;  whether 
it  is  desired  to  prepare  the  gold  for  amalgamation  by  keeping  it 
longer  in  the  mortar,  as  with  'rusty'  gold  requiring  abrasion;  also 
whether  capacity  is  desired  or  the  crushing  is  being  done  for  con- 
centration. 

When  the  discharge  is  kept  as  low  as  possible  without  punching 
or  wearing  out  the  screen  too  fast,  that  is,  with  a  1%  to  2-in.  dis- 
charge, the  greatest  capacity  results,  and  the  sizing  is  more  evenly 
done  up  to  the  point  where  the  screen  openings  are  enlarged  by  the 
violence  with  which  the  pulp  is  forced  through  them.  The  minimum 
of  sliming  is  then  done,  and  consequently  the  low  discharge  is  the 
best  for  concentrating  purposes,  as  it  affords  the  best  opportunity 
for  the  sulphide  liberated  from  the  gangue  to  be  discharged  from  the 
mortar  as  soon  as  crushed  to  the  screen  size,  instead  of  being  crushed 
and  slimed  still  finer,  as  would  be  the  case  with  a  high  discharge. 
The  loss  in  concentration  is  mainly  in  the  slimed  sulphide. 

As  the  height  of  discharge  is  raised,  the  pulp  becomes  finer  and 
is  slimed  more  in  comparison  to  the  size  of  the  screen  used.  A  large 
amount  of  pulp  is  retained  in  the  mortar,  perhaps  two  or  three  times 
as  much  as  with  a  low  discharge,  so  that  the  gold  remains  longer 
subjected  to  the  action  of  the  stamps,  and  has  a  more  prolonged 
contact  with  the  quicksilver  and  plates  inside  of  the  mortar.  The 
gold  also  receives  more  abraiding  and  polishing  by  the  stamps  and 
pulp,  which  may  or  may  not  be  an  advantage,  depending  upon  the 
amenability  of  the  gold  to  amalgamation.  As  this  pulp  is  hnrled 
less  violently  through  the  screens,  and  washes  over  a  lesser  area  of 
the  screen  surface,  and  consists  of  the  upper,  more  dilute,  finer  por- 
tion, the  capacity  is  reduced.  The  sulphide  from  its  higher  specific 
gravity  tends  to  settle  upon  the  die  and  is  crushed  finer  than  the 
gangue  from  which  it  is  liberated. 

This  finer  crushing  of  the  sulphide  increases  with  the  height  of 
discharge  and  the  slowness  of  the  drop.  This  is  seen  in  the  Gilpin 


98  SPLASH   AND   WAVE   MORTARS 

county,  Colorado,  practice  where  a  16-in.  drop,  with  30  drops  per 
minute,  and  a  13-in.  discharge,  together  with  a  wide  mortar,  are 
used  so  that  the  sulphide  may  be  thoroughly  slimed  and  may  thereby 
liberate  its  mechanically-held  gold  for  amalgamation.  Where  con- 
centration is  to  follow  crushing  the  exact  reverse  of  this  practice  is 
used. 

About  I1/*?  in.  is  the  least  amount  of  discharge  height  advisable, 
for  with  a  lower  height  the  pulp  will  usually  bank  against  the  lower 
edge  of  the  screen,  rendering  that  part  inopperative  and  subject  to 
excessive  wear.  A  high  discharge,  5  in.  at  least,  is  necessary  when 
using  a  chuck-block  plate,  that  scouring  of  the  plate  may  not  take 
place.  Where  considerable  wood  enters  the  mortar  with  the  ore,  a 
low  discharge  is  sometimes  used  that  the  wood  may  be  caught 
under  the  stamps  and  thoroughly  reduced  to  pulp  for  passing 
through  the  screen ;  or  a  high  discharge  is  used  where  the  shoes  are 
not  lifted  out  of  the  water  so  that  the  wood  may  collect  in  a  line 
along  the  screen  and  be  removed  by  the  hand  or  a  straining  spoon 
of  wire  introduced  through  a  curtain  or  swinging  wooden  door  above 
the  screen. 

A  mortar  having  a  low  discharge  where  the  faces  of  the  shoes  are 
raised  out  of  the  water  and  pulp  is  violently  splashed  over  the 
screen  surface  is  called  a  'splash'  mortar  or  battery;  while  a  mortar 
having  a  high  discharge  where  the  shoes  are  not  lifted  out  of  the 
water  and  the  pulp  runs  along  the  screen  in  waves  is  said  to  be  a 
'wave'  mortar  or  battery. 

Feeding  the  Mortar. — In  feeding  a  mortar  the  feed  should  be  kept 
'low/  as  can  be  ascertained  by  feeling  the  stem  as  the  shoe  strikes. 
Should  the  stamp  strike  a  well  cushioned  blow,  the  feed  has  been  too 
'heavy,'  and  there  is  too  thick  a  bed  of  pulp  on  the  dies  to  get  the 
maximum  crushing  effect.  Should  it  strike  with  a  jar  or  rebound, 
the  feed  has  been  too  'low,'  and  there  is  too  thin  a  bed  of  pulp  on  the 
dies  to  get  the  maximum  crushing  effect,  or  to  prevent  the  shoe  ana 
die  from  chipping,  and  the  life  of  the  stem  from  being  shortened. 
The  stamp  should  strike  a  hard,  firm  blow,  just  barely  cushioned  on 
the  pulp,  without  jar  or  rebound.  The  beginner  in  feeding  should 
first  set  the  feeder  so  that  it  works  at  every  drop  of  the  feed-stamp 
without  over-feeding  the  mortar,  then  by  adjusting  first  one  way  and 
then  another,  in  connection  with  feeling  the  stem,  a  point  will  be 
found  where  it  is  apparent  to  the  eye  that  the  maximum  that  the 
stamps  can  crush  is  being  delivered  into  the  mortar.  By  feeling 
the  stamps  now,  it  will  be  found  that  they  are  barely  cushioned  on 
the  pulp  from  jar  and  rebound. 


POWER   FACTORS  99 

To  feed  'close'  is  a  millman's  term  meaning  to  feed  very  'low.' 

Power. — The  power  necessary  for  operating  a  stamp-battery  is 
made  up  of  three  factors.  This  first  is  the  nominal  horse-power  re- 
quired to  raise  the  stamps  without  reference  to  friction ;  this  is  the 
power  directly  expended  in  crushing.  By  remembering  that  a  horse- 
power is  the  expenditure  of  33,000  foot-pounds  of  energy  per  minute, 
the  horse-power  can  be  computed  by  multiplying  the  weight  of  the 
stamp  in  pounds  by  the  length  of  drop  in  feet  and  this  by  the  num- 
ber of  drops  per  minute — which  will  give  the  number  of  foot-pounds 
expended  in  lifting  the  stamp  during  a  period  of  one  minute, — and 
then  dividing  by  33,000. 

This  gives  the  following  formula : 

Nominal  horse-power  per  stamp  = 

Weight  of  stamp  in  pounds  X  height  of  drop  in  feet  X  No.  drops  per  minute 

33,000 

As  the  stamp  appears  to  rise  slightly  higher  than  its  drop,  as 
measured  and  computed  when  at  rest,  it  is  best  to  use  the  maximum 
height  of  drop  rather  than  the  average  in  computing.  It  should 
also  be  borne  in  mind  that  the  average  weight  of  stamps  in  use  in 
a  mill  is  not  their  newly-shod  weight,  but  their  newly-shod  weight 
less  one-half  the  difference  in  weight  between  a  new  and  a  dis- 
carded shoe,  and  with  a  further  reduction  due  to  the  tapered  ends 
broken  off  the  stem;  these  two  reductions  may  be  taken  as  ll/2% 
of  a  1000-lb.  stamp. 

The  second  factor  is  the  power-demand  due  to  friction — that  of 
the  stem  in  the  guides,  which  is  small  and  is  mainly  due  to  the  side- 
thrust  of  the  cam  striking  the  tappet  away  from  the  centre  of  the 
stem;  the  friction  of  the  cam  on  the  tappet;  and  the  friction  of  the 
cam-shaft  in  its  bearings.  This  power  requirement  is  somewhat 
variable,  but  according  to  the  generally  accepted  formula  of  Henry 
Louis,  it  amounts,  in  a  10-stamp  battery,  to  20.2%  of  the  nominal 
horse-power  required  to  raise  the  stamps.  The  sum  of  these  two 
powers  is  the  amount  that  must  be  applied  to  the  pulley  of  the 
cam-shaft.  Special  attention  is  called  to  the  fact  that  in  the  litera- 
ture dealing  with  the  computation  of  power  required  by  stamps, 
reference  is  made  to  this  power  only,  which  is  usually  spoken  of  as 
the  theoretical  horse-power. 

The  third  factor  is*  the  power  consumed  by  the  friction  of  the 
driving  belt  between  the  line-shaft  and  the  cam-shaft,  the  belt- 
tightener,  the  line-shaft  itself,  and  by  the  belts  and  intermediate 
shafting  between  the  line-shaft  and  the  source  of  power.  The  power 


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slss  issS  IBIi    I 


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uosOr-        OOOOOO 


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T)-  in  IA,  vo     t-  oo  a< 


Or^i-O  rOi-Ow>  r~< 
lO^^O  OOvO^.f^  ^-< 
1-OOaO  O  —  (S  tO  •*! 


§§§ 


ABNORMAL   LOSS   OF   POWER  101 

consumed  in  the  driving  engine  or  motor  in  overcoming  its  own  fric- 
tion, and  in  the  conversion  of  one  form  of  energy  into  another,  may 
be  included  in  this,  though  properly  it  should  form  a  fourth  part. 
This  third  part  of  the  power  is  extremely  variable,  and  may  range 
from  10  to  40%  of  the  entire  power  consumed.  Consequently  the 
greatest  care  should  be  exercised  in  designing  and  constructing  a 
mill  and  in  selecting  the  machinery,  that  the  amount  of  power  re- 
quired may  be  at  a  minimum  instead  of  expending  a  large  part  in 
uselessly  racking,  wearing,  and  tearing  the  machinery  and  building. 
The  abnormal  loss  of  power  in  this  way  as  observed  in  stamp-mills, 
outside  of  that  lost  in  the  engine  or  motor  (the  type  and  size  of  which 
needs  to  be  carefully  looked  into),  may  occur  from  a  multiplicity  of 
shafts  and  belts,  shafts  located  too  close  together  and  of  too  small  a 
diameter,  narrow  belts  and  pulleys  of  small  diameter,  loose  and  slip- 
ping belts,  belt-tighteners  excessively  tight,  insecure  foundations, 
and  unstable  framework.  When  a  bearing-box  is  running  warm, 
power  is  being  unnecessarily  consumed.  A  change  of  lubricants, 
or  a  change  to  ring  oilers  or  to  constant-drip  oil-cups,  may  effect  a 
saving.  Bearings  having  ring  oilers  should  be  used  wherever  pos- 
sible. Where  a  mill  is.  built  of  green  timber,  the  boxes  will  need 
occasional  readjustment,  owing  to  the  warp  of  the  timber.  Dust 
from  the  breaker  and  from  dumping  ore  in  the  bins  settles  in  the 
cam-shaft  boxes  and  on  the  faces  of  the  cams,  which  increases  fric- 
tion and  the  power  consumed.  The  examination  and  correction  of 
power-losses  is  a  painstaking  task  and  is  often  neglected,  especially 
in  the  smaller  mills,  through  the  losses  not  being  apparent  and  from 
failure  to  realize  the  amount  that  a  small  saving  in  this  direction 
will  reach  in  the  course  of  a  year. 

It  can  be  understood  that  it  is  impossible  to  give  any  accurate 
coefficient  that  will  give  the  sum  of  these  three  parts  of  the  power, 
or  of  the  actual  horse-power  consumed  by  a  battery  having  an  in- 
dependent source  of  power.  It  may  be  approximated  by  saying  that 
in  a  good  installation  of  say  40  stamps,  this  actual  horse-power  con- 
sumed will  amount  to  1.35  of  the  nominal  horse-power  required  to 
raise  the  stamps,  but  that  in  a  small  installation,  or  where  the 
efficiency  of  the  engine  or  motor  is  low,  it  may  amount  to  moi*e  than 
this  figure. 

Individual  Stamp.— Various  types  of  'individual'  stamps  have 
been  brought  to  the  attention  of  the  mining  fraternity,  but  they  have 
been  generally  more  or  less  unsatisfactory,  partly  through  inherent 
defects  in  the  idea,  and  partly  through  the  general  mill  details  being 
poorly  worked  out.  The  first  disadvantage  of  this  type  is  that  they 


102  STANDARD   VS.    INDIVIDUAL  STAMPS 

are  built  in  units  of  2  or  3  stamps  each,  each  unit  requiring  the  same 
space  as  one  standard  5-stamp  battery.  A  summing  of  the  extra 
parts  and  construction  required  to  make  up  with  individual  units 
the  equivalent  of  a  standard  5-stamp  battery  will  show  that  the  cost 
of  the  finished  individual-stamp  mill  may  be  nearly  double  that  of 
the  standard  type  of  the  same  number  of  stamps. 

With  the  quadruple-discharge,  there  are  four  screens  and  one 
feeder  to  each  stamp,  or  20  screens  and  five  feeders  to  be  given  at- 
tention for  each  5  stamps,  in  comparison  to  the  one  large  screen  and 
feeder  of  a  standard  5-stamp  battery.  It  is  impossible  to  keep  an 
even  height  of  discharge  with  the  quadruple-discharge  mortar,  and 
this  results  in  severe  wear  and  tear  on  the  screens  before  the  dies 
are  worn  down.  They  overfeed  easily,  particularly  when  running  on 
fine  ore  and  using  a  short  drop ;  this  may  be  due  to  the  large  screen 
area,  as  the  same  trouble  has  been  noticed  in  the  double-discharge 
5-stamp  mortar,  or  to  the  fact  that  there  are  no  neighboring  stamps 
to  throw  the  pulp  back  on  the  die.  It  is  almost  useless  to  feed  quick- 
silver into  the  mortar  without  it  being  immediately  thrown  out  on 
the  plates,  and  it  is  not  attempted. 

The  great  argument  has  been  the  increased  screen  surface.  This 
cannot  be  denied,  but  in  answer  to  the  question  as  to  whether  it  is 
desirable  or  not,  attention  is  called  to  the  large  number  of  double- 
discharge  mortars  in  use  with  their  back  discharges  closed  up.  In 
the  5-stamp  mortar  there  are  from  500  to  550  blows  struck  per 
minute,  divided  evenly  all  over  the  mortar;  this  results  in  the  pulp 
being  splashed  over  the  screen  surface  all  the  time,  the  whole  length 
of  the  screen  being  in  continuous  use.  Whereas,  in  the  individual 
mortar  there  is  only  one-fifth  the  number  of  blows  and  consequently 
the  screen  surface  is  not  in  continuous  use.  The  action  of  the  pulp 
within  the  mortar  should  be  carefully  studied  in  comparing  the  in- 
dividual stamp  with  the  standard. 

Various  tests  have  been  made  at  different  times  to  test  the  merits 
of  double  discharge  mortars  and  an  excess  of  screen  surface;  the 
results  of  these  point  to  one  conclusion  only,  that  the  standard  form 
of  single-issue  5-stamp  mortar  can  be  made  to  deliver  the  pulp  about 
as  fast  as  made  and  that  an  increased  screen  area  gives  no  increase 
in  capacity. 

The  reports  of  those  using  individual  stamps  in  actual  practice, 
rather  than  experimental  practice,  is  that  they  give  little  if  any  in- 
creased tonnage  over  the  ordinary  stamps.  Where  they  have  been 
run  to  an  advantage  has  been  with  a  large  quantity  of  water  and 
with  heavy  stamps,  conditions  that  are  enabling  the  South  African 


POWER  REQUIRED  BY  INDIVIDUAL  STAMP 


103 


millmen  to  obtain  a  capacity  of  ten  tons  per  stamp  and  upward.  The 
good  showings  in  capacity  and  absence  of  slime  have  been  made  by 
using  a  minus  height  of  discharge  and  with  so  much  trouble  from 
screen  breakages  that  no  experienced  millman  would  attempt  to 
run  a  standard  battery  in  that  way. 

Until  the  claim  of  increased  capacity  is  positively  proved,  it  will  be 


STANDARD    STAMP-BATTERY    MOUNTED    ON    IRON    ANVIL-BLOCKS    AND    THE    INDIVIDUAL 
STAMP-BATTERY. 

contended  that  the  cost  for  power  per  ton  crushed  is  higher  rather 
than  lower  than  with  the  standard  battery,  for  the  reason  that  the 
cam-shaft  of  the  individual  battery  is  identical  with  that  'of  the 
standard,  with  the  exception  that  it  raises  4  or  6  stamps  instead  of 
10.  Consequently  the  power  per  stamp  required  to  drive  the  shaft- 
ing, independent  of  raising  the  stamps,  in  the  individual  mill  is  from 
1%  to  2y2  times  that  required  for  the  standard  battery.  It  is  only 
fair  to  add  that  a  material  increase  in  the  capacity  would  offset  this 
slight  increase  in  power  required  per  stamp. 


104  OPERATING   THE   INDIVIDUAL   STAMP 

The  cost  of  operating  the  individual  stamp  is  much  higher  than 
with  the  standard.  This  is  due  to  the  extra  cost  and  loss  of  time 
from  screen  troubles  and  to  an  excessive  amount  of  general  repair 
work.  Also  from  the  fact  that  they  are  harder  to  operate  than  the 
standard.  In  a  certain  large  individual-stamp  mill  not  practising 
amalgamation,  and  where  the  arrangement  and  construction  was 
good  and  operations  were  well  systematized,  one  batteryman  with 
a  helper  attended  54  stamps — equivalent  to  one  man  running  27 
stamps.  Under  identical  conditions  with  the  standard  type,  one 
batteryman  would  be  running  80  or  .100  stamps.  At  another,  an 
amalgamating  mill  of  the  individual  type  having  18  stamps,  one  man 
was  barely  able  to  handle  the  mill  on  the  evening  and  midnight 
shifts,  and  when  wet  ore  began  interfering  with  the  operation  of 
the  small  feeders,  two  men  were  required  for  these  shifts. 

While  the  individual  stamp  is  a  unit  that  can  be  repaired  without 
stopping  the  adjoining  stamps,  the  loss  of  running  time  in  such  a 
mill  is  actually  greater  than  in  the  standard  mill,  due  to  the  extra 
repairs,  changing  screens,  and  other  work.  There  is  an  extra  loss  of 
time  through  the  increased  number  of  plate  dressings  required  in 
outside  amalgamation — the  number  of  dressings  being  double  that 
required  when  quicksilver  is  fed  to  the  mortars.  The  advantage  of 
the  individual  mortar  is  that  the  feed  of  each  stamp  can  be  regu- 
lated to  get  the  greatest  crushing  effect,  whereas  with  the  standard 
battery  and  a  lazy  millman,  a  few  stamps  in  a  battery  may  be 
dropping  hard  and  crushing  fast  while  the  others  are  being  cush- 
ioned and  crushing  little. 

The  individual  stamp  may  be  advantageous  in  crushing  an  ore  for 
concentration,  the  sulphides  of  which  exhibit  a  tendency  to  slime,  but 
in  most  cases,  and  particularly  where  amalgamation  is  to  be  prac- 
tised, it  cannot  be  recommended.  It  has  been  noted  before  that 
estimates  of  what  a  stamp-mill  will  do  can  be  made  with  exactness, 
but  not  so  with  other  crushing  devices.  This  criticism  will  apply  in 
the  case  of  standard  and  individual  stamps,  for  the  latter  are  usually 
a  disappointment.  In  the  case  of  one  very  prominent  installation,  ex- 
perimental work  was  carried  on  with  a  full-size  working  stamp  over 
a  long  period  of  time  and  an  estimate  was  made  of  the  tonnage  that 
should  be  attained.  After  the  installation  was  made  and  the  han- 
dling of  the  stamps  was  highly  developed,  the  resulting  tonnage 
was  only  76  per  cent  of  the  estimate. 


PART  II 

AMALGAMATION 


CHAPTER  V 

PROPERTIES  AND  CARE  OF  MERCURY — PRINCIPLES  OF  AMALGAMATION — 
INSIDE  AMALGAMATING  PLATES. 

Properties  and  Care  of  Mercury. — Mercury  is  classed  as  a  metal, 
and  as  such  is  unique  in  that  it  is  liquid  at  ordinary  temperatures. 
It  is  commonly  called  quicksilver  on  account  of  its  color  and  activity ; 
in  mills  it  is  also  spoken  of  as  the  'silver'  or  the  'quick.'  It  is  13.6 
times  heavier  than  water.  It  freezes  at -40°F.  (-40°C.).  It  vaporizes 
little  or  not  at  all  at  ordinary  temperatures,  but  the  tendency  to 
vaporize  becomes  greater  with  increase  of  temperature  until  at 
212  °F.  or  the  boiling  temperature  of  water  there  is  danger  of  saliva- 
tion in  approaching  it.  It  boils  at  680°F.  (360°C.).  It  is  insoluble 
in  water,  but  violent  agitation  causes  a  little  of  it  to  be  taken  up 
mechanically  in  a  fine  state  of  division  by  the  water.  It  combines 
chemically  with  certain  substances  to  form  two  series  of  compounds, 
mercurous  and  mercuric — as  mercurous  chloride  (Hg2Cl2)  and  mer- 
curic chloride  (HgCL).  It  combines  mechanically  with  other  metals 
to  form  alloys  called  amalgams,  which  exhibit  some  of  the  charac- 
teristics of  chemical  compounds.  Mercury  is  readily  dissolved  by 
strong  nitric  acid,  and  slowly  by  the  dilute  acid.  It  is  not  dissolved 
by  hydrochloric  acid.  It  is  dissolved  by  hot  concentrated  sulphuric 
acid,  but  not  by  the  cold  acid.  Metallic  mercury  is  slowly  dissolved 
by  weak  or  strong  solutions  of  potassium  cyanide  or  of  sodium 
cyanide;  the  rate  of  dissolution  increasing  with  the  strength  of  the 
solution;  the  compounds  of  mercury  are  more  readily  attacked  by 
these  solutions. 

Mercury  alloys  directly  with  most  of  the  metals  to  form  amalgams. 
When  the  proportion  of  the  mercury  is  small,  these  amalgams  are 
hard,  solid,  and  crystalline ;  as  the  proportion  of  the  mercury  in- 
creases the  amalgam  becomes  pasty,  and  finally  liquid.  Gold  amal- 
gam containing  90%  of  mercury  is  liquid,  with  87^2%  pasty,  and 
at  85%  mercury  the  amalgam  crystallizes.  Gold,  silver,  copper, 
lead,  zinc,  tin,  cadmium,  bismuth,  tellurium,  sodium,  and  potassium 
unite  directly  with  mercury ;  the  latter  two  requiring  heat  to  combine 
actively.  Iron,  especially  when  in  a  fine  state  of  division,  can 
be  caused  to  unite  with  mercury  by  means  of  sodium  amalgam. 

107 


108  FLOURED  AND  SICKENED  MERCURY 

Antimony  and  arsenic  unite  with  mercury  when  heated.  Chromium, 
manganese,  platinum,  aluminum,  and  nickel  will  unite  with  mercury 
by  the  employment  of  the  electric  current  and  by  other  indirect 
means. 

Pure  mercury  is  not  affected  by  the  air  at  ordinary  temperatures, 
but  when  impure,  its  surface  becomes  coated  and  tarnished  with 
compounds  of  the  base  metals,  such  as  oxides,  sulphates,  chlorides, 
and  sulphides,  and  probably  to  some  extent  by  mercuric  oxide  and 
sulphide.  Impure  mercury  can  readily  be  recognized,  since  its  sur- 
face will  appear  tarnished  instead  of  bright,  and  its  globules  will  not 
be  spherical  and  tend  to  unite  quickly  with  one  another  when  brought 
together.  When  rolled  about,  the  globules  will  be  sluggish  and  will 
elongate  to  a  tail  and  leave  a  black  film  behind.  Oils  and  organic 
substances  also  tend  to  render  mercury  impure.  When  it  breaks  up 
into  extremely  minute  globules  which  will  readily  float  on  water, 
it  is  said  to  be  'floured;'  and  when  these  globules  refuse  to  coalesce 
again,  the  mercury  is  said  to  be  'sickened.'  Shaking  the  mercury  in 
the  presence  of  detrimental  substances,  or  stamping  in  the  mortar, 
promotes  'flouring,'  and  in  the  first  case  'sickening'  as  well.  Each 
one  of  the  '  sickened '  globules  of  mercury  is  surrounded  by  a  film  of 
foreign  substance,  quite  often  an  oxide  or  other  compound  of  a  base 
metal. 

Various  methods  are  used  to  restore  impure  or  foul  mercury  to  its 
normal  condition.  Cyanide  of  potassium  is  beneficial  through  neu- 
tralizing the  grease,  and  abstracting  the  oxygen  from  the  oxides. 
Likewise  sodium,  by  its  attraction  for  oxygen,  reduces  the  oxides 
of  the  base  metals  which  are  coating  the  globules  of  mercury ;  and  as 
sodic  oxide  is  soluble  in  water,  it  can  be  removed  by  washing,  while 
the  base  metals  enter  the  mercury  forming  a  base  amalgam.  After 
treatment  with  these  powerful  alkalies  the  mercury  is  in  condition  to 
do  good  work,  but  owing  to  the  tendency  of  the  base  metals  to  again 
oxidize,  the  relief  is  only  temporary ;  consequently  an  attempt  should 
be  made  to  remove  the  base  metals  entirely.  Retorting  will  accom- 
plish this,  if  carried  on  at  moderate  heat,  though  probably  not  com- 
pletely, as  some  of  the  base  metals,  such  lead  and  zinc,  may  distill 
over,  particularly  at  high  heat.  Purification  by  chemical  means  is 
easier  and  better.  This  can  be  accomplished  to  some  extent  by  em- 
ploying sulphuric  acid,  better  by  hydrochloric  acid,  and  still  better 
by-nitric  acid,  the  acid  being  dilute  in  each  case.  For  this  purpose 
the  mercury  should  be  placed  in  a  glass  or  glazed  vessel  that  will 
not  be  attacked  by  the  acid,  with  a  solution  of  one  part  nitric  acid 
and  from  five  to  ten  parts  of  water,  and  allowed  to  remain  for  at 


CLEANSING  MERCURY  109 

least  48  hours  with  frequent  stirrings  that  all  the  base  metals  may 
be  dissolved.  Besides  dissolving  the  base  metals  that  contaminate 
the  mercury,  the  acid  will  also  dissolve  some  of  the  mercury,  and 
should  it  crystallize,  more  water  and  a  little  acid  should  be  added 
that  the  mercuric  nitrate  may  be  kept  in  solution.  The  mercury  in 
solution  as  mercuric  nitrate  will  be  precipitated  when  more  impure 
mercury  is  added,  by  base  metals  replacing  the  mercury  to  form 
nitrates  of  themselves.  By  suspending  a  piece  of  copper  in  the 
solution,  the  mercury  in  solution  can  be  completely  precipitated. 
The  mercury  should  be  washed  to  remove  all  traces  of  the  acid  be- 
fore being  used.  Since  impure  mercury  does  not  amalgamate  gold 
with  the  facility  that  pure  mercury  does,  and  as  it  is  liable  to  become 
'floured'  and  'sickened'  and  thereby  result  in  loss  of  both  gold  and 
mercury,  as  well  as  to  cause  base  metals  to  enter  the  bullion,  the 
purification  of  the  'quick'  should  always  be  given  the  necessary 
attention. 

Principles  of  Amalgamation. — Mercury  'wets'  those  substances 
with  which  it  amalgamates  just  as  water  wets  an  ordinary  sub- 
stance, forming  a  thin  film  of  amalgam  about  them  by  the  absorption 
of  the  mercury.  The  surface  tension  of  mercury  is  very  high  and 
its  tendency  is  to  pull  within  itself,  or  below  the  surface,  any  sub- 
stance that  amalgamates  with  it;  in  this  way  the  particles  of  gold 
arrested  on  an  amalgamating  plate  disappear  below  the  surface. 
In  the  case  of  those  substances  with  which  it  does  not  amalgamate, 
its  surface  tension  acts  negatively  and  it  is  strongly  repellent  to 
them. 

In  crushing  an  ore  for  amalgamation,  the  aim  should  be  to  crush 
just  fine  enough  to  liberate  the  gold  from  its  matrix  of  quartz  or 
other  mineral,  that  these  golden  grains  or  flakes  may  be  exposed  to 
and  caught  by  the  aid  of  mercury.  Crushing  too  coarse  will  result 
in  the  gold  not  being  liberated,  but  still  enclosed  in  the  gangue  rock 
so  that  the  mercury  is  unable  to  reach  it.  Crushing  too  fine  may 
result  in  beating  the  gold  up  into  flakes  so  fine  that  it  can  hardly 
be  brought  into  contact  with  mercury,  or  may  possibly  coat  it  with 
a  film  of  slime  or  some  constituent  of  the  ore  so  that  it  will  not 
readily  amalgamate. 

Mercury  is  fed  into  the  mortar  that  it  may  come  in  contact  with 
the  gold  as  soon  as  liberated  from  the  rock  by  crushing.  The  action 
of  the  stamps  causes  the  mercury  to  become  finely  divided  and  to  be 
intermingled  throughout  the  pulp,  thus  'wetting'  a  considerable 
amount  of  the  gold.  Part  of  this  gold  sinks  about  the  dies  as 
amalgam,  part  is  caught  upon  the  inside  plates  if  any  are  used,  and 


110  CHUCK-BLOCK   PLATE 

part  passes  out  through  the  screen.  That  gold  which  comes  in  con- 
tact with  the  mercury  while  in  the  mortar  and  which  passes  through 
the  screen,  is,  by  virtue  of  its  being  encased  in  an  envelope  of  mer- 
cury or  amalgam,  larger  than  the  original  native  golden  grain  be- 
fore being  coated  by  the  mercury ;  this,  in  connection  with  the  coat- 
ing of  mercury,  enables  the  lip  or  apron  plate  easily  to  catch  it. 
Gold  that  is  not  so  'wetted'  is  harder  to  catch  and  may  travel 
farther  away  from  the  mortar. 

Inside  Amalgamating  Plates. — The  part  of  the  gold  which  is  won 
from  the  mortar-sand  is  found,  not  in  the  sand  resting  on  the  dies 
when  the  mortar  is  opened,  but  in  that  below  the  level  of  the  face 
of  the  dies.  Where  no  mercury  is  fed  to  the  mortar,  this  will  be 
as  coarse  gold,  but  where  mercury  is  fed  into  the  mortar,  it  will  be 
found  as  amalgam.  The  amount  of  gold  retained  in  the  mortar- 
sand  will  vary  with  the  time  the  gold  has  been  accumulating  in  the 
mortar  and  with  the  height  of  discharge.  A  wide  mortar  with  a 
high  discharge  carries  double  or  treble  the  amount  of  pulp  a  narrow 
mortar  with  a  low  discharge  will  carry.  In  such  a  '  wave '  mortar  it 
will  be  hard  for  the  coarse  gold  and  amalgam  to  escape  as  their 
higher  specific  gravity  will  cause  them  to  sink  down  through  the 
pulp  rather  than  to  rise  and  pass  out  through  the  screen,  while  in 
the  'splash'  mortar  they  will  be  thrown  through  the  screen  with 
little  regard  to  their  specific  gravity.  The  amount  of  gold  retained 
in  the  mortar  will  also  vary  with  the  size  of  the  particles  of  gold; 
thus,  with  fine  gold  there  will  be  very  little  caught  in  the  mortar- 
sand,  while  with  coarse  gold  the  percentage  will  be  relatively  high. 

The  'chuck-block'  is  a  piece  of  wood  fastened  to  a  strip  of  the 
same  material,  the  latter  resting  beneath  the  screen  in  the  screen- 
frame  slots  of  the  mortar.  Its  purpose  is  to  fill  a  portion  of  the 
surplus  space  between  the  dies  and  the  mortar  lip  and  screen  frame. 
The  chuck-block  is  sometimes  lined  with  a  copper  amalgamating 
plate,  called  a  'front  inside  plate'  or  'chuck-block  plate.'  Its 
function  is  to  catch  and  hold  upon  its  surface  as  much  gold  in  the 
form  of  a  hard  amalgam  as  possible.  On  account  of  its  close 
proximity  to  the  stamps,  this  plate  is  subjected  to  much  scouring 
action  by  the  pulp,  which  increases  as  the  chuck-block  is  moved 
nearer  the  stamps,  or  the  height  of  discharge  is  lowered,  so  that 
mortars  for  using  inside  plates  were  formerly  designed  to  be  from 
14  to  18  inches  across  the  inside  of  the  mortar  at  the  lip.  Chuck- 
block  plates  are  now  very  successfully  used  in  narrow  mortars  only 
12  in.  wide  at  the  lip  by  using  a  high  discharge.  The  height  of  the 
chuck-block  can  be  varied  by  inserting  beneath  it  and  in  the  screen- 


MAKING   A   CHUCK-BLOCK  111 

frame  slots,  strips  of  wood  of  varying  thickness,  usually  1  in.,  and 
these  may  be  removed  as  the  die  wears  down,  thus  maintaining  the 
height  of  discharge  uniformly  with  reference  to  the  top  of  the  die. 
Most  mills  have  two  heights  of  chuck-blocks  on  hand,  the  higher 
one  being  used  with  new  dies,  and  the  lower  one  substituted  after 
the  dies  are  worn  down. 

The  common  form  of  a  curved  chuck-block  is  apparently  wrong, 
for  it  is  this  curved  part  or  'belly'  that  is  in  the  best  position  to  be 
scoured.  A  good  method  of  making  a  chuck-block  is  to  take  a 
piece  of  2  by  6-in.  sugar  pine  and  rip  it  diagonally  across  the  ends, 
making  two  triangular  sectional  lengths.  Attach  one  of  these  to 
the  strip  that  rests  in  the  screen-frame  slot  by  bolts  a  foot  apart, 
using  a  piece  of  strap-iron  in  connection  with  these  bolts  to  hold  the 
lower  end  of  the  plate  in  position  and  as  a  protection  against  its 
being  torn  loose.  If  the  strip  of  iron  used  is  from  14  to  %  in.  thick, 
the  amalgam  will  accumulate  advantageously  along  the  upper  side 
of  this  iron  rib  and  in  the  angle  formed  by  it  with  the  copper  plate. 
Scouring  can  largely  be  prevented  by  protecting  the  plate  with  a 
heavy  wire  screen  of  quarter  or  half-inch  mesh,  spaced  from  the 
plate  by  a  nut  on  each  bolt  that  attaches  this  screen  to  the  chuck- 
block. 

A  copper  plate  is  sometimes  bolted  to  the  back  of  the  mortar, 
this  is  called  a  'back  inside  plate.'  On  account  of  its  location  it  is 
hard  to  handle  and  to  get  at,  and  consequently  is  seldom  used. 
These  'inside  plates'  were  formerly  used  in  nearly  all  mills,  while 
today  they  are  used  very  little ;  the  tendency  of  modern  milling  is 
to  eliminate  them  entirely.  A  chuck-block  plate  can  be  'run'  in  the 
narrow  mortar,  twelve  inches  wide  at  the  lip,  generally  used  today, 
by  employing  a  sufficiently  high  discharge  and  considerable  care. 
A  back  plate  can  be  used  in  these  mortars  if  it  can  be  set  six  inches 
above  the  dies.  It  should  be  bolted  through  the  mortar  and  have 
two  sets  of  bolt  holes,  that  it  may  be  adjusted  to  the  wear  of  the  dies. 

These  inside  plates  are  usually  of  raw  copper  3/16  to  Y4  in.  thick, 
that  they  may  not  easily  be  dented  or  worked  out  of  shape  and  may 
stand  the  excessive  wear.  As  they  are  cleaned  of  the  amalgam  by 
being  chiseled  and  are  liable  to  be  scoured,  silver-plating  is  an  un- 
necessary expense.  They  are  cleaned  every  10  to  30  days  on  low- 
grade  ore.  Where  the  mortar-sand  is  not  removed  at  this  time,  an 
extra  chuck-block  is  kept  on  hand  and  is  merely  substituted  for  the 
enriched  block  after  being  burnished  and  dressed  with  mercury. 
These  plates  must  be  carefully  watched.  They  are  especially  hard 
to  start  and  may  give  the  amalgamator  some  anxiety  before  a  film 


112  CARE  OP  INSIDE  AMALGAMATING  PLATES 

)f  amalgam  is  deposited  over  the  whole  plate.  No  bare  spots  should 
be  allowed  as  they  tend  to  spread. 

The  inside  plates  should  not  be  kept  soft  or  the  amalgam  will 
slough  off,  neither  should  the  amalgam  be  kept  hard  to  the  point  of 
being  brittle,  for  such  amalgam  will  not  withstand  the  action  of  the 
moving  pulp  to  the  extent  that  a  softer,  more  tenacious,  slightly 
yielding  one  will,  nor  so  readily  catch  the  gold  and  amalgam.  When 
using  inside  plates,  mercury  is  fed  to  the  mortar  according  to  the 
appearance  of  the  lip  plate  on  the  outside  of  the  mortar  and  an 
occasional  examination  of  the  inside  plates,  usually  that  on  the 
chuck-block.  This  examination  of  the  chuck-block  can  be  made 
without  removing  the  screen,  by  using  a  canvas  curtain  instead  of 
a  board  to  close  the  opening  in  the  mortar  above  the  screen;  the 
feed  water  is  shut  off  and  as  soon  as  the  water  is  stamped  out  of 
the  mortar,  the  stamps  are  hung  up ;  a  small  stream  of  water  is  run 
along  the  screen  to  wash  off  the  chuck-block,  when  the  curtain  is 
removed  and  the  plate  inspected.  Should  there  be  a  bare  spot,  it  is 
burnished  and  a  little  mercury  or  soft  amalgam  is  well  rubbed  in. 
After  some  experience  the  amalgamator  is  able  roughly  to  judge  the 
condition  of  the  amalgam  by  reaching  in  with  his  hand  and  feeling 
the  amalgam  without  stopping  the  battery.  When  using  inside  plates 
the  greatest  care  should  be  exercised  that  the  feed  is  kept  just  right 
and  that  no  over-feeding  or  choking  of  the  mortar  occurs.  For  this 
purpose  careful  chuck-block  operators  remove  the  splash  board 
from  in  front  of  the  screen,  that  any  change  in  the  splash  or  wave 
of  the  pulp  may  be  readily  discernible ;  over-feeding  is  indicated  by 
a  line  of  pulp  appearing,  'banking,'  at  the  lower  edge  of  the  screen 
and  gradually  rising.  The  feed  of  quicksilver  must  also  be  watched, 
not  alone  in  reference  to  the  amalgamating  in  general,  but  also  that 
the  amalgam  on  the  inside  plates  may  not  become  too  hard  or  too 
soft  and  thereby  lost. 

The  use  of  inside  plates  increases  the  saving  of  gold  inside  the 
mortar,  by  catching  and  holding  a  large  part  that  would  otherwise 
pass  out  through  the  screen.  This  was  formerly  considered  desira- 
ble practice,  but  the  use  of  narrow  mortars,  heavy  stamps,  and  low 
discharge  have  individually  and  collectively  made  good  inside  plate 
work  difficult,  so  that  the  sentiment  is  now  against  their  use.  The 
two  claims  made  in  their  favor  are:  that  they  should  be  used  when 
running  on  high-grade  ore  with  the  idea  that  the  smaller  the  amount 
of  amalgam  to  be  handled  on  the  outside  plates  (referring  especially 
to  the  apron  plates),  the  smaller  the  loss  will  be;  and  that  by  their 
use  fine  or  refractory  gold  can  be  caught  that  cannot  otherwise  be 


SCOURING   OF    CHUCK-BLOCK   PLATE  113 

saved.  The  arguments  against  their  use  are :  that  they  necessitate 
a  high  discharge  which  cuts  down  capacity  and  may  cause  over- 
stamping  ;  and  that  they  place  the  gold,  or  rather  the  amalgam, 
where  it  can  be  easily  scoured  off  and  lost  should  the  mortar  over- 
feed. On  opening  a  mortar  that  has  been  overfed,  and  has  run 
choked  for  some  time,  the  upper  part  of  the  chuck-block  plate  will 
usually  be  found  to  be  freshly  scoured,  sometimes  down  to  the  cop- 
per. This  scoured  amalgam  being  hard  and  dry,  has  been  found 
difficult  to  arrest  on  the  outside  plates  unless  they  are  quite  wet 
with  mercury,  consequently  some  of  the  amalgam  passes  beyond 
the  plates  and  traps  and  is  lost. 

Inside  plates  should  only  be  used  where  it  is  proved  that  more 
gold  can  be  caught  by  their  use  than  without  them,  and  such  cases 
will  be  rare.  In  all  ordinary  cases,  more  gold  will  be  saved  per 
ton,  a  greater  tonnage  crushed,  and  more  satisfaction  in  operating 
obtained  without  their  use.  When  they  are  needed,  it  would  appear 
well  to  employ  both  a  front  and  back  plate  with  the  idea  of  getting 
all  the  advantage  there  may  be  in  their  use ;  usually  there  is  no  back 
plate  on  account  of  the  trouble  and  inconvenience  due  to  its  posi- 
tion ;  moreover,  a  back  plate  cannot  be  placed  in  most  of  the  mortars 
used  today. 


CHAPTER  VI 

SPLASH  AND  LIP-PLATES — APRON-PLATE — DRESSING  AND  CARE  OP 
APRON-PLATE  —  FEEDING  MERCURY  —  DRY  AMALGAMATION  — 
OUTSIDE  AMALGAMATION — AMALGAMATION  IN  CYANIDE  SOLU- 
TION— WATER  REQUIRED  IN  AMALGAMATION — TEMPERATURE  OF 
BATTERY  WATER — PERIOD  BETWEEN  PLATE  DRESSING. 

Splash  and  Lip-Plates. — The  'splash-plate'  is  placed  in  front  of 
the  screen,  being  fastened  to  the  mortar  or  to  the  battery  posts,  so 
that  the  pulp  flowing  or  splashing  through  the  screen  may  fall  or 
impinge  upon  it,  run  down  its  surface,  and  drop  on  the  head  of  the 
'lip-plate,'  which  is  a  copper  plate  resting  on  the  lip  of  the  mortar 
and  held  in  place  by  the  chuck-block,  the  screen  frame,  or  other- 
wise. The  splash-plate  is  attached  to  the  'splash-board'  or  answers 
the  purpose  of  a  splash-board,  which  is  to  catch  and  confine  the  wet 
pulp  as  it  comes  splattering  through  the  screen  instead  of  allowing 
it  to  fall  promiscuously  about  the  front  of  the  mortar.  The  advisa- 
bility of  the  splash-plate  is  a  matter  of  individual  opinion  usually, 
and  it  is  not  used  in  all  cases.  The  conditions  under  which  work  is 
largely  done  today  are  with  a  fine-grained  gold,  a  low-grade  ore, 
and  a  required  large  capacity,  necessitating  a  narrow  mortar  and 
low  discharge,  which  in  general  prohibit  the  successful  use  of  inside, 
plates,  or  of  the  catching  of  much  gold  in  the  mortar-sand.  The 
amalgam  on  the  splash  and  lip-plates  is  hard,  with  little  tendency 
to  run  and  slough  off,  or  to  granulate  and  break  away,  consequently 
here  is  a  good  place  to  hold  it — a  better  place  than  on  the  inside 
plates,  or  on  the  apron  plates,  but  not  as  good  as  in  the  mortar-sand. 
Various  forms  of  splash-plates  are  in  use.  Besides  that  the  pulp, 
after  passing  through  the  screen,  shall  impinge  upon  this  plate  and 
run  down  to  the  upper  part  of  the  lip-plate,  the  general  requirement 
is  that  they  be  easily  handled  when  necessary  to  remove  them  to 
open  the  mortar,  and  that  in  connection  with  the  lip-plate  they  pre- 
sent a  large  surface. 

The  function  of  the  lip-plate  is  the  same  as  that  of  the  splash- 
plate,  to  catch  and  hold  the  particles  of  'wetted'  gold  and  amalgam 
that  have  passed  through  the  screen,  and  consequently  their  pur- 
pose, condition,  arid  treatment  is  in  every  way  similar.-  Due  to  the 
hardness  and  dryness  of  the  amalgam  on  these  splash  and  lip- 

114 


DISTRIBUTING   BOX 


115 


plates,  it  is  supposed  that  but  little  native  gold,  without  any  wet- 
ting of  mercury,  is  caught  here,  since  there  is  no  surplus  mercury 
to  wet  the  particles.  The  amalgam  on  the  lip  and  splash-plate  is 
always  found  to  be  a  little  harder  than  that  on  the  inside  plates. 
The  lip-plate  is  as  long  as  the  mortar  lip  on  which  it  rests  and 
ordinarily  six  to  seven  inches  wide,  which  is  entirely  too  narrow. 
Every  mortar  should  be  so  built  that  a  distributing  or  collecting 


NEVADA   HILLS    MILL   OF    1600-LB.    STAMPS    AT   FAIRVIEW,    NEVADA. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 


box  can  be  fitted  to  it  at  the  lip.  This  is  an  iron  box  bolted  to  the 
mortar  to  extend  the  lip.  It  gives  a  firm  backing  to  the  lip-plate 
which  may  be  as  much  as  18  in.  wide.  These  boxes  distribute  the 
pulp  across  the  head  of  the  apron  plates  through  from  8  to  16  holes, 
so  that  by  plugging  up  some  of  the  holes,  if  necessary,  an  even  distri- 
bution can  be  secured  where  the  discharge  is  not  uniform  across  the 
full  length  of  the  screen.  They  form  a  projection  over  the  apron- 
plates,  preventing  leakage ;  and  by  not  requiring  close  contact  with 
the  mortar,  prevent  the  apron-table  from  being  jarred. 

The  lip  and  splash-plates  are  burnished  and  dressed  with  mer- 


116  CARE   OF   SPLASH   AND   LIP-PLATES 

cury  when  put  in  position  after  being  cleaned  up.  They  receive  no 
further  dressings  unless  their  surfaces  become  fouled  with  some  base 
metal  such  as  zinc,  lead,  or  babbitt  that  has  accidentally  fallen  into 
the  mortar,  or  by  some  constituent  of  the  ore  itself.  In  such  case 
the  plates  will  receive  a  stiff  brushing  to  remove  the  foul  film,  and 
all  loose  material  on  the  plates  will  be  collected  and  saved  for  treat- 
ment at  ciean-up  time.  The  lip  and  splash-plates  have  their  amalgam 
chiseled  off  semi-monthly  when  running  on  low-grade  ore.  An  extra 
lip-plate  is  kept  on  hand  that  the  battery  need  not  be  stopped  longer 
than  to  make  the  change.  Like  the  inside  plates,  unsilvered  copper 
is  the  most  advisable  for  the  lip  and  splash-plates.  The  lip-plate  is 
subjected  to  considerable  abuse  and  should  be  i/4  in.  thick,  while 
y$  in.  may  be  considered  sufficient  for  the  splash-plate. 

Apron-Plate. — Following  the  lip-plate  and  independent  of  the 
mortar  is  the  'apron-plate,'  mounted  on  a  platform  called  a  'table,' 
usually  built  of  wood.  This  plate  is  slightly  wider  than  the  lip-plate 
and  from  8  to  28  ft.  long  and  sometimes  longer,  in  which  case  they 
are  built  in  two  or  more  sections  in  series.  The  apron-plate  is  not 
intended  for  catching  the  bulk  of  the  gold,  except  where  no  mercury 
is  fed  to  the  mortar,  but  more  particularly  for  that  which  has  escap- 
ed being  caught  on  the  plates  above.  Consequently  it  is  given  the 
greatest  care  and  attention  to  keep  it  in  good  condition  to  catch 
gold.  The  flow  of  the  pulp  on  the  apron-plate  is  distributed  in  such 
manner  as  to  best  enable  each  particle  to  come  in  contact  with  the 
plate.  Sufficient  mercury  is  kept  on  it  to  render  the  amalgam  soft 
enough  to  wet  any  amalgamable  gold  that  may  come  in  contact  with 
it;  while  the  amalgam  is  kept  bright  and  in  an  active  condition  by 
frequent  dressings  of  the  plate.  The  idea  is  that  it  shall  be  in  the 
best  condition  to  catch  gold  that  has  not  been  wetted  by  quicksilver, 
no  matter  if  quicksilver  is  fed  to  the  mortar  or  not. 

It  is  in  the  care  of  the  apron-plate  that  the  amalgamator  takes 
his  greatest  pains  and  pride.  Here  is  found  a  striking  difference  in 
the  ideas  and  methods  of  different  millmen.  Some  keep  the  apron- 
plate  hard,  even  to  the  verge  of  the  amalgam  breaking  away  and 
the  lower  end  of  the  plate  becoming  quite  blue  in  appearance,  for  the 
purpose  of  preventing  the  mercury  from  working  down  the  plate 
into  the  mercury  trap  at  the  foot  of  the  plate  and  eventually  into 
the  creek  below.  These  are  said  to  be  amalgamate  'dry,'  as  the  plate 
is  kept  comparatively  dry  of  mercury.  Others  keep  the  amalgam 
soft  and  plastic,  sometimes  overfeeding  mercury  or  dressing  the 
plate  so  soft  that  the  mercury  separates  from  the  amalgam  and 
collects  in  globules,  'tears/  which  work  down  the  plate  carrying  a 


117 


! 


118  WET   AMALGAMATION 

little  gold  with  it  into  the  traps  from  which  a  part  of  it  will  usually 
be  lost.  This  is  said  to  be  'wet'  amalgamation,  as  the  plate  is  kept 
wet  or  moist  with  mercury. 

A  coarse,  easily  amalgamated  gold  will  be  readily  caught  on  a 
hard  plate,  but  fine  gold  requires  a  soft,  plastic  sheet  of  amalgam. 
A  hard  plate  is  not  as  active  in  catching  gold  as  a  soft  one,  since  it 
cannot  so  readily  wet  the  gold,  and  the  surface  tension  in  absorbing 
the  gold  into  and  below  the  surface  of  the  amalgam  is  not  so  great 
on  account  of  the  amalgam  being  crystalline.  The  coarse  gold,  be- 
cause of  its  greater  weight,  sinks  through  and  is  dragged  along  the 
bottom  of  the  film  of  pulp,  coming  in  repeated  contact  with  the 
amalgamated  plate  beneath,  so  that  with  coarse  gold  this  plate  need 
not  be  so  active  in  wetting  and  catching  it.  Whereas  the  fine  gold 
is  carried  along  distributed  throughout  the  pulp  and  only  occasion- 
ally comes  in  contact  with  the  plate,  consequently  the  plate  should 
be  in  the  best  condition  to  wet  the  gold  at  the  first  contact.  The 
coarse  gold  is  more  liable  to  be  wetted  in  the  mortar,  and  when  in 
such  condition  should  be  quickly  arrested,  even  on  a  hard  plate. 
If  a  particle  of  hard  amalgam  or  of  gold  is  brushed  over  a  hard,  dry 
amalgamated  surface,  it  will  probably  not  be  caught,  but  if  brushed 
over  a  soft,  wet  spot  it  will  quickly  attach  itself  to  the  amalgamated 
surface.  This  leads  to  the  inference  that  wet  plates  are  the  best 
amalgamators.  By  keeping  them  soft  they  form  the  best  amalga- 
mating surface,  but  if  the  narrow  margin  of  safety  is  overstepped, 
the  mercury  will  separate  out  of  the  amalgam  and  run  off,  carrying 
with  it  some  of  the  gold  with  which  it  has  amalgamated,  and  herein 
is  the  difficulty  with  wet  amalgamation.  Given  an  easily  amalgama- 
ted ore,  the  amalgamator  may  approach  dry  amalgamation  and  save 
the  greater  time  and  attention  required  for  wet  amalgamation  with- 
out increasing  the  loss  in  the  tailing. 

Dressing  and  Care  of  Apron-Plate. — In  cleaning-up  and  dressing 
the  apron-plate  where  wet  amalgamation  is  practised  or  the  plates 
are  kept  reasonably  soft,  some  mercury  is  first  sprayed  on  the  plates 
where  needed — usually  the  head  of  the  table  where  considerable 
amalgam  has  collected.  The  mercury  is  well  rubbed  into  the  amal- 
gam by  means  of  a  stiff  whisk  broom  that  is  worn  down  or  cut  off. 
The  amalgam  is  loosened  and  softened  down  to  the  silvered  surface 
of  the  plate.  It  is  usual  with  wet  amalgamation  to  remove  part  of 
the  amalgam  once  daily  when  treating  an  average  ore,  so  that  a 
constant  amount  remains  to  keep  the  plate  in  good  working  condi- 
tion, taking  off  no  more  on  clean-up  day  than  on  any  other  day. 
The  part  of  the  amalgam  to  be  removed  is  now  pushed  up  to  one 


PLATE   DRESSING 


119 


place  at  the  head  of  the  plate  by  a  whisk  or  a  'rubber' — a  piece  of 
pure  rubber  or  rubber  belting  3  by  5%  by  V2  in.  thick — where  it  is 
taken  up  by  a  scoop.  The  plate  is  now  well  rubbed  again,  that  the 
amalgam  may  be  thoroughly  softened  down  to  the  silvered  surface 


fee 


•<  ft 
a  o 


with  a  view  to  preventing  the  formation  of  a  hard  film  or  scale  of 
amalgam ;  that  the  consistence  and  texture  of  the  amalgam  may  be 
such  as  is  desired ;  that  the  mercury  in  the  amalgam  may  be  more 
evenly  distributed  and  more  securely  held  by  it;  and  that  the 
amalgam  may  be  worked  into  an  active  condition.  The  amalgam 


120  PLATE   DRESSING 

is  now  distributed  evenly  across  the  plate  so  that  there  is  con- 
siderable soft  amalgam  at  the  head  of  the  table,  very  little  on  the 
middle  section  of  the  table,  and  none  on  the  foot  which  is  kept 
fairly  hard  to  catch  any  mercury  or  soft  amalgam  running  down 
from  above.  Finally,  the  amalgam  is  smoothed  or  'bedded  down' 
across  the  plate  and  at  right  angles  to  the  flow  of  the  pulp  by  using 
a  soft  and  long-straw  whisk  broom.  The  practice  of  riffling  or 
roachmg  across  the  soft  amalgam  has  been  condemned  by  some  as 
wrong  for  the  reason  that  these  riffles  catch  the  fine  iron  and  steel 
from  the  mortar  and  the  heavier  sulphide  from  the  ore,  and  thus 
coat  or  foul  the  amalgamating  surface.  The  fact  that  these  tiny 
grooves  do  act  thus,  speaks  well  for  their  function  in  catching  gold. 
However,  these  riffles  can  be  avoided  by  smoothing  the  surface  of 
the  amalgam  with  a  fine-haired  paint  or  calcimining  brush.  An 
experiment  should  be  conducted  by  brushing  one  side  of  a  plate 
crosswise  and  the  other  side  lengthwise  to  the  flow  of  the  pulp.  Care 
is  used  that  all  particles  of  amalgam  are  well  set,  for  this  reason 
many  amalgamators  finally  run  the  brush  up  and  down  on  each  side 
of  the  table  where  there  is  liable  to  be  loose  amalgam  in  the  corners. 

Some  amalgamators  use  considerable  refinement  in  their  methods 
and  claim  that  a  whisk  for  rubbing  and  a  rubber  for  scraping  the 
amalgam  are  injurious  to  the  silver  plating.  They  use  for  these  pur- 
poses a  rag,  often  a  pad  of  blanket  cloth.  A  rag  requires  more  labor 
to  use  and  is  harder  on  the  hands  than  a  brush,  so  that  whisk 
brooms  are  commonly  used.  For  carrying  the  tools  used  in  dressing 
the  plates  and  for  holding  the  amalgam  recovered,  a  deep  iron  kettle 
is  used,  or  sometimes  a  gold-pan.  For  spraying  the  mercury  on  the 
plates,  a  strong  bottle  with  a  piece  of  canvas  or  a  double  thickness 
of  muslin  tied  over  the  mouth  is  used.  Suitable  bottles  may  be  made 
of  iron  by  screwing  a  cap  over  one  end  of  a  IVu  or  2-in.  pipe  of  a 
few  inches  in  length.  Mercury  is  also  tied  up  in  a  canvas  bag  in 
quantity  about  the  size  of  an  egg;  such  a  bag  is  kept  in  a  cup  to 
prevent  loss  of  the  mercury. 

The  amalgam  in  wet  amalgamation,  especially  that  on  the  first 
plate,  should  be  of  such  consistence  that  it  can  be  pushed  up  with 
the  finger  and  remain  without  flattening  out ;  that  it  will  be  soft  and 
plastic  like  putty ;  that  the  brush  lines  do  not  run  or  disappear ; 
that  it  does  not  run  or  slough  down  the  plate,  as  indicated  by  its 
being  caught  lower  down  than  usual  and  piling  up  at  the  drops  be- 
tween plates ;  and  that  no  tears  of  mercury  appear  or  hang  to  the 
edges  of  the  individual  plates.  The  idea  is  to  keep  the  plate  as  wet 
as  possible  without  losing  any  of  the  mercury  or  amalgam.  The 


121 


P  i> 

i  8 

.1  -* 


122  AMALGAMATION    METHODS 

loss  of  mercury  carrying  away  gold  is  the  main  argument  against 
wet  amalgamation  and  the  greatest  care  and  study  should  be  given 
to  prevent  any  abnormal  loss  and  yet  keep  the  plate  moist.  In  ap- 
pearance this  amalgam  should  look  neither  hard  and  dead  from 
too  little  mercury,  nor  like  a  mirror  from  an  excess,  but  have  a  white 
frosted  appearance.  It  has  been  said  that  the  plate  should  have 
the  appearance  of  a  silver  dollar;  this  is  correct  if  the  kind  of  a 
dollar  is  stated.  The  peculiar  whitish  lustre  of  a  newly-minted  silver 
coin  is  the  appearance  the  amalgam  should  have;  but  should  the 
amalgam  appear  like  the  ordinary  silver  coin  that  has  lost  its  'youth- 
ful bloom,'  it  is  too  hard,  too  dead,  too  crystalline  for  the  good 
amalgamation  of  gold  that  is  in  a  fine  state  of  division  or  that  is 
at  all  difficult  to  catch. 

Feeding  Mercury. — The  apron-plate  is  examined  at  its  head  at 
intervals  of  one-half  to  two  hours,  usually  hourly,  clearing  it  by 
means  of  a  stream  of  water  for  the  purpose  of  learning  how  amalga- 
mation is  progressing  and  how  much  mercury  must  be  fed  into  the 
mortar.  At  first  the  amalgamator  will  press  or  mark  the  amalgam 
with  his  finger  to  learn  its  consistence,  but  in  a  short  time  wrill  be 
able  to  tell  by  its  appearance  alone.  After  examining  the  plate, 
mercury  is  fed  into  the  mortar ;  the  amount  being  judged  by  the 
appearance  of  the  plate.  It  should  be  sufficient  to  keep  the  plate  in 
good  condition  until  the  next  examination.  Should  the  plate  upon 
this  inspection  have  its  amalgam  of  the  proper  consistence  and  be 
wet  with  mercury  to  the  proper  point,  a  normal  amount  of  mercury, 
as  indicated  by  experience  with  that  ore,  is  fed  to  the  mortar ;  should 
the  amalgam  appear  hard  and  dry,  an  extra  amount  of  mercury  is 
fed ;  should  the  plate  appear  too  soft  and  wet,  no  mercury  is  added 
that  it  may  harden  to  the  right  condition  by  the  time  of  the  next 
examination. 

For  feeding  the  mercury  into  the  mortar,  an  amalgamator's  spoon 
is  used  to  measure  it  from  a  cup.  This  spoon  is  of  wood,  much  like 
a  mustard  spoon ;  the  bowl  is  bored  or  burned  in  it  to  hold  mercury 
to  the  size  of  a  small  pea.  The  amalgamator  throws  the  quicksilver 
into  the  mortar  through  the  feed  slot  at  the  back,  a  half  or  full  spoon 
or  more,  according  to  the  amount  he  considers  necessary  from  the 
appearance  of  the  plates.  Some  head  amalgamators  make  use  of  a 
chart  having  a  blank  space  for  each  battery,  and  write  on  these 
blanks  the  amount  of  mercury  to  be  fed  to  each  mortar  by  their 
assistants  on  the  different  shifts.  This  is  an  unsatisfactory  method 
and  seldom  found,  for  even  an  inexperienced  man  can  learn  under 
instruction  in  a  short  time  to  feed  mercury  properly. 


ESTIMATING    BULLION    FROM    MERCURY   FEED 


123 


The  mercury  is  weighed  each  morning  to  ascertain  the  amount 
fed  to  the  mortars  during  the  previous  day.  After  the  plates  have 
become  saturated  with  mercury  and  loaded  with  what  may  be  termed 
their  constant  of  amalgam,  the  amalgamator  divides  the  ounces  of 


bullion  recovered  during  a  stated  period  by  the  number  of  ounces 
of  mercury  fed  to  the  mortars  during  that  time.  This  result  be- 
comes a  factor  by  which  he  estimates  the  amount  of  gold  amalga- 
mated each  day  and  from  this  what  the  month's  run  should  be. 


124  INDICATOR   OF    MERCURY    REQUIRED 

With  an  amalgamator  who  uses  care  in  feeding  mercury  and  a  gold 
that  does  not  vary  greatly  in  the  size  of  its  particles,  this  is  a  fairly 
accurate  factor  and  a  satisfactory  method,  being  equal  to  the  hap- 
hazard methods  of  sampling,  assaying,  and  estimating  that  obtain 
in  many  mills. 

While  it  is  well  to  inform  the  amalgamator  whether  low,  medium, 
or  high-grade  ore  is  being  put  into  the  mill,  he  makes  but  little  use 
of  this  information  except  in  corroboration  as  it  is  so  often  unrelia- 
ble, and  he  is  also  unable  to  know  when  this  ore  of  a  different  nature 
is  going  to  reach  the  mortars.  At  the  hourly  examination  of  the 
plates  he  is  able  to  see  how  much  amalgam  is  being  deposited  or 
built  up  on  the  plates,  and  this  is  a  true  index  of  the  gold  content  of 
the  ore,  unless  it  has  suddenly  become  base  or  unamalgamable.  When 
mercury  is  fed  in  the  right  quantity  and  at  the  proper  intervals, 
very  little  additional  mercury  is  required  in  dressing  the  plates. 
Where  inside  plates  are  used,  the  lip  is  used  as  the  outside  indicator 
of  the  amount  of  mercury  to  be  fed  to  the  mortar  to  keep  the  inside 
plates  in  condition ;  should  the  apron-plate  become  dry,  a  little  mer- 
cury can  be  sprayed  on  the  dry  spots  at  the  head  of  the  table  from  a 
bottle  or  bag  without  stopping  the  battery.  If  one  side  of  the  plate 
is  dry  and  the  mercury  is  fed  to  that  end  of  the  mortar,  the  larger 
part  will  come  out  on  that  side  if  the  mortar  is  of  the  splash  or  low- 
discharge  type. 

Amalgam,  or  mercury  containing  gold,  has  a  greater  attraction 
for  gold  than  mercury  alone.  Mercury  that  has  the  gold  only  partly 
strained  out  of  it  is  better  for  amalgamating  than  gold-free  mercury. 
A  bed  of  gold  amalgam  is  a  most  active  catcher  of  gold — superior 
to  silver  amalgam — and  the  plates  should  always  be  covered  with 
it.  Amalgam  acts  tenaciously  in  holding  the  mercury  on  the  plates. 
New  plates  dressed  with  mercury  do  not  give  the  best  results  until 
a  bed  of  amalgam  has  spread  over  them,  as  has  been  proved  by 
sampling  and  assaying  the  pulp  after  passing  over  plates  when  in 
this  condition.  Consequently  close  clean-ups  with  chisels  should  be 
avoided  unless  some  of  the  amalgam  is  returned  to  the  plates.  Such 
clean-ups,  however,  in  connection  with  thoroughly  rubbing  and 
softening  the  amalgam,  prevents  the  formation  of  hard  layers  of 
amalgam,  but  the  close  'skinning'  of  the  plate  is  detrimental  to  the 
silver-plating,  and  some  amalgamators  will  not  use  even  a  rubber  for 
removing  the  amalgam. 

Dry  Amalgamation. — Where  'dry'  amalgamation  is  practised,  the 
procedure  does  not  differ  materially.  In  dressing  the  plates,  no  ef- 
forts are  made  to  soften  the  bottom  part  of  the  amalgam  or  to  keep 


WET   VS.    DRY   AMALGAMATION  125 

it  soft  in  comparison  with  the  silver-plated  surface ;  the  efforts  being 
confined  to  putting  the  surface  of  the  amalgam  in  good  condition  for 
catching  the  gold.  Any  soft  amalgam  that  may  be  considered  as 
surplus  is  removed,  or  only  that  which  loosens  and  breaks  away  in 
the  dressing,  the  '  crumbs, '  is  removed ;  the  balance  being  allowed  to 
remain  and  become  hard  until  the  monthly  or  semi-monthly  clean- 
up, when  it  is  removed  by  being  chiseled  and  scraped  off,  care  being 
used  not  to  reach  into  the  silver-plating.  After  the  chiseling,  mer- 
cury is  rubbed  in  to  soften  the  remaining  amalgam,  which  is  scraped 
together  by  a  'rubber.'  At  many  of  the  mills  where  dry  amalgama- 
tion is  in  vogue,  the  plates  are  'sweated'  at  intervals  by  pouring 
boiling  water  on  them,  or  by  placing  a  cover  of  wood  or  blankets 
over  them  and  turning  steam  or  boiling  water  in  underneath.  This 
results  in  loosening  the  film  of  hard  amalgam  that  will  always  form, 
especially  when  amalgamating  dry,  so  that  it  may  be  scraped  and 
scaled  off  if  at  once  attacked.  A  large  amount  of  gold  that  would 
be  otherwise  locked  up  on  the  plates  is  secured  by  'sweating,'  but 
it  is  destructive  to  the  silver-plating  and  dangerous  on  account  of 
the  possibility  of  salivating  the  workmen.  The  paternal  laws  of 
Australia  prohibit  approaching  a  'sweated'  plate  until  after  the  lapse 
of  a  certain  length  of  time,  which  makes  the  'sweat'  of  little  avail. 
A  wet  sponge  should  be  worn  at  the  nostrils  when  there  is  danger  of 
salivation. 

As  to  the  relative  merits  of  wet  and  dry  amalgamation,  dry  amal- 
gamation answers  where  the  gold  is  coarse  and  easily  amalgamated, 
and  as  it  require  less  labor  and  attention,  and  usually  entails  a 
smaller  loss  of  mercury,  it  may  be  advisable  in  some  cases.  As  the 
gold  becomes  finer  and  more  difficult  to  amalgamate,  the  necessity 
of  amalgamating  wet  increases.  The  life  and  good  condition  of  the 
plates  is  increased  by  amalgamating  under  the  wet  conditions  de- 
scribed. Where  amalgamation  is  done  entirely  outside,  the  plates 
should  be  kept  wet,  certainly  wetter  than  is  usual  with  dry  amalga- 
mation, since  the  gold,  not  being  wetted  in  the  mortar,  will  have  a 
tendency  to  slip  farther  over  the  dry  surface. 

The  amalgamator  should  make  tests  on  each  ore  to  determine  the 
relative  merits  of  wet  and  dry  amalgamation  for  that  particular 
ore,  by  running  a  'wet'  and  'dry'  plate  side  by  side.  Possibly  the 
percentage  of  sulphide  may  have  some  bearing  on  the  way  the 
amalgamation  should  be  conducted,  through  the  scouring  effect  of 
the  heavy  sulphide  or  the  tendency  of  the  sulphide  to  foul  the  plate. 

Outside  Amalgamation. — Where  the  mercury  is  fed  inside  the 
mortar  with  the  object  that  the  particles  of  gold  may  be  wetted  and 


126  OUTSIDE   AMALGAMATION 

that  sufficient  mercury  may  come  through  the  screen  in  the  form  of 
amalgam,  or  in  a  finely  divided  state,  to  keep  the  'outside'  plates 
in  proper  condition,  they  are  said  to  practise  '  inside  amalgamation, ' 
though  formerly  this  term  had  more  particular  reference  to  catch- 
ing and  holding  the  gold  on  the  inside  of  the  mortar.  Where  no 
mercury  is  fed  to  the  mortar,  but  all  is  added  on  the  outside  plates, 
and  the  gold  comes  through  the  screens  as  native  gold  unwetted 
by  mercury,  they  are  said  to  practise  '  outside  amalgamation. ' 

Outside  amalgamation  involves  no  radical  departures  from  the 
general  methods  of  plate  amalgamation  when  mercury  is  fed  to  the 
mortar.  Lip  and  splash-plates  are  dispensed  with,  all  the  gold  being 
caught  on  the  apron-plates.  A  common  fault,  where  outside  amalga- 
mation is  practised,  is  that  the  plates  are  dressed  too  wet  and  then 
allowed  to  become  too  dry  before  dressing  again.  This  can  be 
avoided  and  the  plate  kept  in  condition  by  sprinkling  at  intervals 
as  required  a  little  mercury  from  a  bag  on  the  dry  spots  at  the 
head  of  the  table  without  stopping  the  battery,  but  it  must  be  care- 
fully done.  The  greater  part  of  the  coarse  gold  can  often  be  caught 
on  the  first  12  in.  of  the  plate  surface  if  mercury  is  dropped  on  as  re- 
quired. When  mercury  is  not  fed  as  needed  and  the  plate  becomes 
hard  and  coated,  as  quickly  happens  when  treating  rich  ore,  the 
gold  will  tend  to  slip  over  the  dry  part  and  be  caught  lower  down. 
As  the  gold  is  not  brought  into  intimate  contact  and  wetted  with 
mercury  in  the  mortar,  longer  plates  covered  with  a  greater  length 
of  the  soft  amalgam  which  is  so  active  in  catching  gold  may  be 
required  than  with  inside  amalgamation.  With  outside  amalgama- 
tion the  plates  will  usually  be  dressed  from  two  to  three  times  as 
often  as  when  the  mercury  is  fed  through  the  mortar.  Outside 
amalgamation  is  interesting  and  affords  excellent  opportunity  to 
study  plate- work ;  some  experience  with  it  will  cause  the  amalgama- 
tor to  incline  toward  wet  amalgamation. 

As  to  whether  outside  or  inside  amalgamation  should  be  the 
practice  is  properly  dependent  on  the  ore  and  the  crushing  machin- 
ery, as  indicated  by  the  amount  of  mercury  lost,  the  increase  or  de- 
crease in  the  amount  of  gold  saved,  and  the  ease  with  which  amalga- 
mation can  be  conducted;  but  in  most  cases  the  prevailing  local 
custom  is  followed  without  testing  the  merits  of  the  other  method. 
Outside  amalgamation  is  followed  with  individual  stamps  as  any 
mercury  fed  to  the  mortars  is  immediately  thrown  out,  so  that  the 
wetting  of  the  gold  and  the  even  feed  of  mercury  to  the  plates  can- 
not be  effected.  The  stamping  of  the  mercury  in  the  mortar  com- 
minutes it  into  fine  globules;  moreover,  the  tendency  of  mercury  in 


OUTSIDE   VS.    INSIDE   AMALGAMATION  127 

the  presence  of  water  and  agitation  is  to  form  small  globules  to  some 
extent  which  are  carried  away  mechanically  in  this  finely  divided 
condition.  This  natural  tendency  of  the  mercury  to  'flour'  is  in- 
creased when  it  is  impure,  or  is  in  association  with  deleterious  sub- 
stances in  the  ore,  so  that  great  loss  may  result  from  either  of  these 
causes.  With  a  clean  ore,  the  loss  of  mercury  in  the  practice  of  inside 
amalgamation  is  usually  about  double  that  occurring  when  doing 
outside  work,  and  with  ores  containing  substances  that  are  detrimen- 
tal to  the  mercury,  the  loss  may  be  five  or  six  times  as  great.  It  is 
impossible  to  say  how  much  gold  is  carried  off  by  this  vagrant  mer- 
cury, but  it  should  be  less  than  that  indicated  by  assaying  the  mer- 
cury caught  in  a  newly  cleaned  mercury  trap,  as  the  larger  part 
must  be  lost  in  the  form  of  finely  divided  mercury  that  has  amal- 
gamated with  but  little  gold.  Oil  and  grease,  taleose  and  clayey  ores, 
arsenic  and  the  compounds  of  arsenic  and  antimony  are  the  worst 
enemies  to  amalgamation — coating  the  floured  mercury  with  a  film 
so  that  it  becomes  permanently  floured,  in  which  condition  it  is  said 
to  be  'sickened.'  Oil  and  grease  are  particularly  bad  and  every 
effort  should  be  made  to  prevent  them  from  coming  in  contact  with 
the  ore,  or  mortar,  or  the  plates.  When  constituents  of  the  ore  coat 
the  plates  and  foul  them  against  amalgamation,  as  much  amalgama- 
tion as  possible  should  be  obtained  in  the  mortar. 

Amalgamation  in  Cyanide  Solution. — Amalgamation  in  cyanide 
solution  presents  no  difficulties  within  the  requirements  made  on  it 
— a  close  saving  on  the  plates  not  being  essential.  The  loss  of  mer- 
cury is  high  as  it  is  dissolved  to  be  precipitated  in  the  ore  and  in  the 
zinc  box.  Most  silver  ores  and  some  gold  ores  contain  base  elements 
which  unite  with  and  destroy  cyanide  to  an  undesirable  extent.  The 
mercury  unites  with  or  replaces  some  of  these  elements,  in  the  latter 
case  forming  a  compound  of  mercury  and  cyanide  which  is  an  active 
solvent  of  gold  and  silver.*  When  the  solution  is  again  brought  in 
contact  with  the  ore,  the  precious  metals  are  dissolved  and  replace 
the  mercury  which  is  precipitated  in  the  ore.  The  mercury  thus 
plays  an  important  and  beneficial  part,  but  only  a  small  amount  of 
mercury  is  utilized  in  this  way,  the  greater  part  being  precipitated  in 
the  zinc  box.  This  deposition  on  the  zinc,  if  not  too  excessive,  ap- 
pears to  assist  the  precipitation  of  the  gold  and  silver,  due  to  the 
formation  of  a  galvanic  couple.  The  mercury  cannot  be  recovered 
economically  under  ordinary  conditions.  The  strength  of  the  solu- 
tion should  be  kept  down  to  one-half  pound  of  potassium  cyanide  per 

*See  'Textbook  of  Cyanide  Practice'  by  the  Author. 


128  AMALGAMATION    IN    CYANIDE   SOLUTION 

ton  of  solution  to  prevent  the  too  rapid  dissolution  of  the  plates  and 
mercury,  though  a  solution  of  two-pound  strength  has  been  success- 
fully used.  As  the  life  of  the  plates  is  limited  to  from  six  to  nine 
months  and  the  amalgamation  rather  roughly  carried  on,  silver- 
plating  the  plates  is  an  inadvisable  expense.  No  aids  or  methods  of 
prolonging  the  life  of  these  plates  have  yet  come  into  use,  notwith- 
standing that  the  item  for  renewals  is  an  important  one.  The  lower 
plate  and  lower  part  of  each  plate  is  eaten  through  first.  As  the 
amalgam  is  cleaned  up  the  closest  from  these  places,  it  gives  weight 
to  the  natural  conclusion  that  a  thick  coating  of  hard  amalgam  would 
prolong  the  life  of  the  plates.  The  cyanide  keeps  the  plates  beauti- 
fully free  from  stains  as  it  dissolves  the  copper  compounds  as  fast  as 
formed,  and  owing  to  its  low  strength  does  not  harden  the  plates  to 
the  extent  that  might  be  expected.  The  plate  tables  should  be  built 
water  tight  that  neither  the  mercury  nor  solution  may  run  through, 
for  the  plates  are  eaten  through  irregularly  and  it  may  not  be  con- 
venient to  remove  them  when  the  first  spot  appears.  In  fact  it  is 
the  custom  to  repair  the  first  spots  or  bare  places  by  tacking  pieces 
of  old  plates  over  them. 

Iron  tables  or  those  having  the  bed  of  plate-iron  or  steel  and  water 
tight  would  be  excellent.  Raw  copper  plates  of  extra  thickness  with 
backs  covered  with  a  thoroughly  solution-proof  paint,  in  two-foot 
sections  with  a  drop  between  each,  the  sections  to  be  easily  and  in- 
dependently removable  or  changeable,  are  the  lines  along  which  these 
tables  should  be  designed.  The  plates  should  not  be  allowed  to  pro- 
ject beyond  their  backing  as  the  ends  are  gradually  dissolved  down 
to  dangerous  knife  edges.  The  solution  being  weak  does  not  injure 
the  hands  of  the  workmen,  though  it  may  make  them  rough  at  times. 
Rubber  gloves  are  not  required.  In  designing  and  building  a  mill 
for  crushing  in  cyanide  solution,  every  effort  should  be  taken  to 
prevent  the  leaking  and  spilling  of  the  gold-bearing  solution,  while 
the  floors  should  be  arranged  to  catch  and  carry  any  such  solution 
to  a  sump  tank.  The  loss  from  this  source  is  high  in  some  mills. 

Water  Required  in  Amalgamation. — For  amalgamating  on  the 
apron-plate,  the  feed  water  used  in  the  mortar  should  be  just  suffi- 
cient to  carry  the  pulp  down  the  table  in  waves  that  appear  retard- 
ed, almost  but  never  stopping,  rolling  over  and  over  and  breaking 
up,  that  each  part  and  particle  of  the  pulp  may  be  brought  in  con- 
tact with  and  dragged  over  the  amalgamated  surface  of  the  plate 
as  much  as  possible.  The  coarse  gold  sinks  to  the  bottom  of  the  pulp 
and  is  caught,  usually  on  the  upper  section  of  the  plate,  within  2  or 
3  ft.  of  the  mortar  lip,  while  the  fine  gold  is  carried  along  by  the 


USE   OF   WATER   IN   AMALGAMATION  129 

sweep  and  rush  of  the  pulp,  and  being  unable  to  sink  through  it, 
must  wait  until  the  turning  over  and  breaking  up  of  the  pulp  finally 
brings  it  in  contact  with  the  plate.  A  difference  has  been  noticed  in 
the  proportion  of  the  gold  to  the  silver  in  amalgam  caught  at  the 
head  of  the  table  as  against  that  caught  at  the  foot.  This  has  been 
credited  to  the  greater  ease  with  which  gold  is  amalgamated  than 
silver,  but  a  sizing  of  the  gold  particles  in  the  ore  might  reveal  that 
the  fine  gold  caught  farther  away  from  the  mortar  contains  a  higher 
proportion  of  silver. 

Where  difficulty  is  experienced  in  amalgamating  the  gold,  or 
where  the  plates  appear  to  be  too  short,  less  water  should  be  used 
in  the  mortar,  even  if  the  grade  of  the  plates  has  to  be  increased, 
that  the  pulp  may  be  dragged  and  rolled  over  the  plates  rather  than 
sluiced.  The  fall  of  plates  now  in  use  varies  from  1^  to  3  in.  per 
foot,  and  should  not  be  less  than  1%  or  2l/±  in.  A  low  fall  requires 
too  much  water  in  the  mortar  that  the  pulp  may  not  bank  on  the 
plates  to  give  good  apron-plate  amalgamation,  especially  if  the  ore 
contains  much  sulphide  or  other  heavy  material.  It  is  better  to 
make  the  grade  too  great  than  too  little.  There  are  various  methods 
of  constructing  plate  tables  that  allow  the  grade  to  be  easily  changed, 
and  it  is  well  to  use  such  construction.  Where  the  pulp  has  banked 
on  the  plate,  the  careful  amalgamator  does  not  hose  it  off  with  a 
large  volume  of  water,  thereby  losing  any  gold  caught  in  the  pulp 
or  only  lightly  attached  to  the  plate,  or  any  spikes  of  crystalline 
amalgam ;  he  turns  on  a  light  stream  and  slowly  and  gently  washes 
the  deposit  away.  Some  millmen  place  a  stick  of  wood  diagonally 
on  the  plate  above  a  bank  of  sand,  diverting  the  stream  of  pulp,  and 
thus  washing  the  sand  away. 

It  was  customary  years  ago  to  use  a  spray  of  clear  water  from  a 
perforated  pipe  or  distributing  box  at  the  head  of  the  table  to  slight- 
ly retard  the  pulp  and  to  cause  the  gold  to  settle  and  attach  itself 
to  the  plate.  The  crushing  capacity  at  that  time  was  small,  due  to 
light  stamps  and  wide  mortars,  but  with  the  reverse  of  these  condi- 
tions now,  all  the  water  that  it  is  safe  to  use  should  be  introduced 
through  the  mortar  in  the  effort  to  pass  the  material  through  the 
screen  as  fast  as  possible.  Wherever  extraordinarily  long  plates  are 
required,  it  will  be  found  that  an  excess  of  water  is  being  used,  or 
that  the  gold  is  extremely  fine.  Where  extra  plates  are  needed  or 
much  amalgam  is  caught  on  the  last  plate  due  to  an  excess  of  water, 
the  pulp  should  be  divided  between  two  short  extra  tables  rather 
than  one  long  extra  table.  This  will  induce  the  rolling  of  the  pulp 
and  the  thinning  of  its  layer,  both  so  necessary  to  facilitate  contact 


130  SCOURING   OF   APRON-PLATE 

of  the  finer  particles  of  gold  with  the  amalgamated  surface  and  good 
plate  amalgamation.  Where  the  plates  are  so  long  that  the  lower 
plate  scours,  and  much  mercury  is  required  to  keep  it  in  condition, 
while  it  returns  no  amalgam,  the  plates  may  be  shortened,  or  the 
use  of  more  water  in  the  mortar  can  be  tried.  The  last  should  cause 
the  gold  to  be  caught  lower  down  and  the  lower  plates  to  keep  in 
condition,  while  the  amalgamator  can  salve  his  conscience  for  this 
departure  from  good  amalgamating  practice  by  the  increased  ton- 
nage due  to  the  use  of  a  larger  quantity  of  water. 

A  plate  requires  the  constant  addition  of  mercury  and  gold  to 
keep  it  from  being  denuded  by  the  pulp.  Running  on  dumps  of  ex- 
tremely low-grade  ore,  as  is  so  often  done  before  the  final  shutting 
down  of  a  mill,  has  been  unsatisfactory  in  many  instances  for  the 
above  reason.  Also,  coarse  crushing  is  generally  resorted  to  in  the 
effort  to  compensate  for  the  low  value  of  the  rock  by  increasing  the 
tonnage,  whereas  the  gold  is  usually  finer  and  may  require  finer 
crushing  to  liberate  it.  Should  the  plates  scour  when  running  on 
this  low-grade  rock,  a  small  amount  of  water  should  be  used  in  the 
mortar  to  induce  the  gold  to  be  amalgamated  on  a  short  length  of 
plate,  while  removing  the  lip  and  splash-plates  may  assist  in  keep- 
ing the  apron-plates  in  condition.  Clear  water  will  carry  off  mercury 
and  amalgam  and  when  allowed  to  run  over  a  plate  for  some  time, 
the  amount  should  be  reduced  to  just  sufficient  to  keep  it  wet  and 
prevent  oxidation  and  discoloration. 

Temperature  of  Battery  Water.— Many  experiments  have  been 
made  with  varying  temperatures  of  battery  water,  and  the  best  re- 
sults have  been  secured  when  it  is  at  a  temperature  between  45  and 
70°F.  (7  to  21°C.).  Below  that  temperature  the  amalgam  tends  to 
become  hard  and  crystalline,  and  poor  amalgamation  may  result, 
though  the. heating  of  the  feed  water  is  seldom  attempted.  Above 
70°F.  the  amalgamation  of  the  gold  upon  the  plates  appears  to  be 
promoted,  but  the  amalgam  becomes  so  liquid  that  it  is  hard  to  re- 
tain it  on  the  plates,  much  of  it  running  down  into  the  traps.  Amal- 
gamating in  water  of  either  an  unusually  high  or  low  temperature 
bears  a  certain  analogy  to  amalgamating  wet  and  dry.  A  high 
temperature  causes  any  acidity  of  the  battery  water  or  the  ore  to 
act  more  vigorously  in  staining  the  plates  by  the  formation  of 
various  compounds  with  the  copper.  The  amalgamator  usually 
manages  to  do  good  work  with  water  of  either  a  high  or  low  tempera- 
ture by  keeping  the  amalgam  at  the  proper  consistence,  but  where 
the  water  has  a  considerable  variation  of  temperature  during  the 
twenty-four  hours,  it  is  impossible  to  vary  the  practice  accordingly. 


CONDITIONS   REQUIRING   PLATE   DRESSING  131 

Period  Between  Plate  Dressing. — How  often  shall  the  plates  be 
dressed?  Just  as  often  as  needed  to  keep  them  in  good  condition. 
Where  the  conditions  are  not  greatly  variable  this  will  be  reduced 
to  dressing  at  stated  periods,  generally  12  hours  apart.  Where  the 
ore  is  low  grade,  'plating'  $1.50  to  $3  per  ton,  the  plates  are  dressed 
once  daily  in  the  morning,  though  the  night  shift  may  soften  and 
dress  the  upper  plate  of  each  apron  if  it  becomes  hard.  This  refers 
to  a  large  mill,  in  a  small  mill  two  dressings  will  be  made  daily,  even 
if  the  plates  are  in  fair  condition,  on  the  principle  of  giving  the 
night  amalgamator  something  to  do.  With  ore  amalgamating  $4 
to  $8,  two  or  three  dressings  will  usually  be  made  during  the  twenty- 
four  hours,  while  with  rich  ore  they  occur  a  few  hours  apart.  The 
clean-up  of  the  amalgam  is  made  when  the  plates  are  dressed  in  the 
morning.  At  the  time  of  other  dressings  only  the  loose  crumbs  of 
amalgam  are  removed  unless  the  ore  is  rich.  The  plates  should  be 
rubbed  sufficiently  to  secure  an  even  texture  of  the  amalgam,  in 
theory  stopping  short  of  the  silver-plating,  while  allowing  as  little 
of  the  hard  scale  to  form  as  possible.  The  amalgam  should  be 
worked  into  its  most  active  condition  with  a  view  to  catching  gold, 
and  further  rubbing  is  superfluous.  Two  men  will  dress  a  plate  16 
ft.  long  in  from  5  to  12  minutes,  depending  on  the  care  and  refine- 
ment used.  Jhe  grade  of  ore  is  not  the  only  factor  determining  the 
number  of  dressings.  The  appearance  of  stains,  or  the  coating  of 
the  plate  by  galena  or  other  sulphides,  or  by  the  semi-amalgamation 
of  tellurium  or  some  base  metal,  will  at  once  call  for  a  dressing  to 
remove  the  fouling  substance.  Plates  that  have  been  treated  with 
strong  cyanide  solution  do  not  hold  mercury  well,  and  some  time 
after  the  dressing  the  mercury  may  collect  in  drops,  or  tears,  that 
work  down  the  plate,  when  the  plate  is  said  to  'run,'  and  should 
be  dressed  at  once. 


CHAPTER  VII 

CONSTRUCTION  AND  ARRANGEMENT  OP  APRON  TABLE — ACCESSORIES  TO 
THE  APRON  TABLE — PLATES  AWAY  FROM  MORTAR — SILVERED 
.  OR  KAW  COPPER  PLATES  AND  THEIR  HANDLING — RECOVERING 
GOLD  FROM  OLD  PLATES — CHEMICALS  AND  THEIR  USE — UNSAT- 
ISFACTORY BARE  AND  HARD  PLATES — CLEANING  AMALGAM  AND 
THE  CLEAN-UP. 

Construction  and  Arrangement  of  Apron  Table. — The  plate  table 
should  be  as  free  from  jar  as  possible,  preferably  carried  up  from 
the  ground  independent  of  the  flooring  and  framework  of  the  mill. 
It  has  been  claimed  that  the  jar  is  beneficial  in  promoting  amalgama- 
tion and  attention  has  been  called  to  the  excellent  work  following 
the  apron-plates  of  shaking  plates  mounted  on  vanner  concentrators 
from  which  the  belts  have  been  removed,  or  similar  mechanisms. 
The  motion  these  shaking  plates  receive  is  an  even,  gentle,  vanning 
motion  like  that  which  causes  the  gold  to  settle  in  the  gold  pan ; 
while  the  vibration  to  which  a  plate  table  is  subjected  from  coming 
in  contact  with  the  mortar,  or  from  the  jar  of  the  floor,  in  a  poorly 
built  mill,  is  quite  different — one  that  causes  the  mercury  to  exude 
from  the  amalgam  in  globules,  and  the  amalgam  to  granulate. 

Plate  tables  are  commonly  built  of  1%  and  2  in.  plank,  laid  either 
lengthwise  or  transversely,  with  side  pieces  of  the  same  material  10 
to  12  in.  wide.  A  better  method  is  to  use  2  by  4,  4  by  4,  or  3  by  5  in. 
planed,  well-seasoned  lumber,  placed  lengthwise  of  the  table,  either 
spiked  together  or  bolted  across  the  width  of  the  table  every  three 
feet,  and  put  together  with  a  thick  waterproof  paint.  With  such  a 
table  there  should  be  no  leakage.  When  drops  are  introduced  they 
are  made  shallow,  the  material  being  cut  out  as  required.  The  sup- 
ports beneath  should  be  as  simple  as  possible,  except  where  rendered 
complicated  by  introduction  of  means  for  changing  the  grade.  The 
table  should  be  dressed  down  to  make  the  center  1/e  in.  lower  than 
the  edges,  or  the  pulp  will  riffle  toward  each  side  of  the  table  forming 
washes  there  and  leaving  it  too  shallow  in  the  centre. 

Drops  between  the  plates  are  introduced  as  the  gold  tends  to  col- 
lect where  the  pulp  strikes  the  plate ;  also,  the  farther  the  pulp 
travels  down  a  straight  plate,  the  greater  its  speed  becomes,  one  of 
the  visible  indications  of  which  is  the  increased  size  of  the  waves  at 

132 


DROPS  IN  APRON  TABLE 


133 


the  loAver  end  of  the  table.  A  drop  serves  to  start  the  pulp  off  anew 
and  prevent  the  acceleration  of  the  speed  of  the  pulp,  wherefore 
it  is  preferable  to  decrease  the  grade  of  the  lower  end  of  the  table  if 
drops  are  not  used.  A  drop  also  breaks  the  flow  of  the  waves,  there- 
by giving  the  fine  float  and  suspended  gold  a  better  opportunity  to 
come  in  contact  with  the  plate,  and  also  induces  a  more  even  distri- 
bution of  the  pulp.  As  the  amalgam  piles  up  at  these  drops,  they 
are  much  in  favor;  the  general  idea  being  that  by  increasing  the 
number  of  drops,  the  length  of  the  plates  may  be  diminished.  This 


j«tf-H  I  -1  1 

MM   | 

I  I.IHM  1 

2-x4.-^ 

4"X  6" 

I*'"' 

4«X6"  Posr 
Con  foe  made  ac/jus 

1 

rab/e 

,                   Copper  P/are                         ) 

li 

H^f: 

i 

_ 

1 

—  .— 

3       E 

Z± 
.  _  . 

3 

AMALGAMATING    TABLE. 


idea  is  not  entirely  correct,  for  the  amount  of  amalgam  collected  at 
these  drops  will  depend  largely  upon  how  the  amalgamation  is 
being  conducted.  Where  too  much  mercury  has  been  used  in  dress- 
ing the  plates  or  fed  through  the  mortar,  the  amalgam  will  run  and 
slough  off  and  collect  at  these  drops,  so  that  the  amalgamator  when 
examining  the  plates,  should  also  use  the  drops  as  an  indicator. 
About  the  only  objection  to  drops  is  that  they  interfere  to  a  slight 
extent  with  the  quick  dressing  of  the  plates.  For  this  reason  a 
single  copper  plate  12  ft.  long  is  often  used.  A  very  nice  apron 
plate  consists  of  one  4-ft.  length  of  raw  or  silvered  copper,  followed 
by  a  drop,  and  finally  a  12-ft.  length  of  silvered  copper.  A  drop 


134  PLATE   DRESSING   WHILE   STAMPING 

of  one-half  inch  is  sufficient  to  give  the  desired  results,  and  more 
than  three-quarters  of  an  inch  is  liable  to  cause  scouring.  Where 
a  drop  scours,  a  strip  of  wood  should  be  used  as  a  baffle-board  to 
ease  the  pulp  to  the  plate. 

Blankets  can  be  placed  underneath  the  plates  if  necessary  to  even 
up  the  table.  The  sides  of  the  plates  should  be  turned  up  and  the 
ends  slipped  well  under  one  another  that  neither  the  water  nor  the 
mercury  may  work  through  to  the  floor.  It  is  preferable  to  have 
the  plates  held  down  by  side  strips  and  overlapping  without  the  use 
of  screws,  which  become  loose  or  partly  destroyed  by  rusting  or 
electrolysis  so  that  they  interfere  in  cleaning  and  dressing  the  plate. 
Designing  the  tables  so  that  the  plate  adjacent  to  the  mortar  may 
be  rolled  away  from  the  mortar  and  over  the  remaining  part  of 
the  table,  or  that  the  entire  table  may  be  moved  forward,  is  an 
unnecessary  expense,  as  advantage  of  this  is  only  taken  when  re- 
moving a  mortar  or  repairing  a  mortar  block. 

At  many  mills  running  on  low-grade  ore,  or  where  the  gold  is 
largely  in  the  sulphide,  it  is  customary  to  clean  and  dress  the  plates 
without  stopping  the  battery,  thus  saving  the  considerable  labor 
involved  in  hanging  up  the  stamps  and  the  loss  of  duty  in  stopping 
the  battery.  This  can  be  easily  and  satisfactorily  accomplished  by 
dividing  the  plate  into  two  sections  by  placing  a  strip  of  wood  per- 
manently down  the  center,  and  directing  the  entire  flow  to  either 
half  of  the  plate  by  plugging  the  holes  on  one-half  of  the  distribut- 
ing box,  usually  also  cutting  down  the  amount  of  water  entering 
the  mortar.  If  no  distributing  box  can  be  bolted  to  the  mortar,  the 
plate  table  can  be  built  so  that  a  wooden  trough  distributer  can  be 
set  beneath  the  lip  of  the  mortar.  At  the  Empire  mill,  Grass  Valley, 
California,  the  tables  are  so  fitted  to  the  mortars  that  when  dressing 
a  plate,  a  launder  of  sufficient  size  and  length  to  carry  the  flowing 
pulp  to  the  plate  of  an  adjoining  battery  is  inserted  under  the  mortar 
lip.  At  first  sight  it  would  appear  that  overloading  a  plate  in  this 
manner  would  be  bad  practice,  but  the  actual  experience  has  been  so 
satisfactory  that  experiments  by  sampling  and  assaying  the  tailing 
under  the  different  conditions  should  be  made  before  condemning 
this  practice  at  any  mill.  Mills  using  these  systems  generally  have 
long  plates.  In  view  of  the  Empire  mill  practice,  it  should  be  possi- 
ble to  deflect  the  pulp  to  a  launder  or  pipe  leading  to  an  extra  plate 
set  over  the  concentrating  floor  or  at  the  side  of  the  mill,  and  this 
has  been  arranged  for  in  a  few  mills. 

Accessories  to  the  Apron  Table. — At  one  time  'sluice-plates'  were 
in  vogue.  Following  the  lip-plate  and  mortar  was  one  apron-plate 


TREASURE-BOX  135 

the  width  of  the  mortar  and  4  ft.  long.  The  plate  table  was  then 
narrowed  down  to  hold  three  or  four  plates  of  half  the  width  of  the 
apron-plate.  Only  the  heavier  gold  and  amalgam  could  sink  down 
through  the  flood  to  which  the  pulp  was  contracted  while  running 
over  these  plates,  also  the  tendency  of  the  pulp  to  scour  the  plates 
was  increased.  These  sluice-plates  were  extensively  used  at  one 
time,  but  have  been  entirely  discarded. 

The  pulp  falling  from  the  last  apron-plate  is  collected  by  a  'tail- 
box'  delivering  to  a  mercury  trap  or  launder.  The  tail -box  should 
be  fitted  with  what  is  known  as  a  'treasure-box.'  This  is  simply 
another  or  second  compartment  in  addition  to  the  one  collecting  the 
pulp  for  the  launder;  a  swinging  door,  or  lid,  enables  the  pulp  from 
the  plate  to  be  directed  to  either  compartment.  The  plate  is  washed 
down  with  a  heavy  stream  of  water,  preparatory  to  dressing,  into 
this  second  compartment ;  after  dressing,  the  plate  is  again  washed 
down,  this  time  with  a  light  stream.  The  function  of  the  treasure- 
box  is  to  catch  the  particles  of  loose  amalgam  that  might  otherwise 
be  lost,  and  also  the  rich  sulphides  that  have  attached  themselves  to  • 
the  plate  by  reason  of  the  amalgamating  of  an  exposed  face  of  con- 
tained gold.  This  box  is  very  necessary  when  running  on  rich  ore. 
A  portable  trough  box  that  can  be  set  beneath  the  lower  edge  of 
the  plate  is  used  to  serve  the  same  purpose.  The  treasure-box  is  a 
handy  accessory  when  the  mortar  is  opened,  as  the  pulp  and  rock 
that  always  litter  the  mortar  lip  and  upper  apron-plate  at  such 
times  is  sluiced  into  the  box  to  be  returned  to  the  mortar  without 
getting  into  the  traps  or  on  the  concentrators.  A  combination 
treasure-box  and  mercury  trap  can  be  made  by  simply  placing  a 
partition  or  baffle  in  a  wide  tail-box,  so  that  the  pulp  from  the  table 
is  caught  in  the  first  compartment  to  overflow  the  baffle  into  the 
second  compartment  leading  into  the  launder. 

A  plate  should  be  tried  in  the  tail-box,  in  the  launders,  and  on 
the  distributing  box  of  the  concentrators,  but  these  plates  must  be 
dressed  at  intervals  and  kept  in  good  condition  to  enable  them  to 
catch  anything.  Riffles  should  be  placed  in  the  launders  or  made  by 
notching  the  bottom  plank  of  the  tailing  flume,  as  even  with  the 
most  careful  amalgamating  a  little  amalgam  escapes  which  can  be 
occasionally  gathered  from  them  without  expense. 

Patent  amalgamators  placed  following  the  apron-plate  have  been 
successful  in  many  instances,  but  it  does  not  appear  wherein  they 
are  superior  to  plates  except  that  they  may  present  a  larger  amalga- 
mating surface,  opposed  to  which  is  the  more  refined  manipulation 
that  can  be  practised  on  the  ordinary  plate.  It  is  better  to  make 
a  trial  of  them  rather  than  an  outright  purchase.  Too  often  such 


136  AMALGAMATING   AWAY   FROM    MORTAR 

machines  do  not  get  a  fair  test,  due  to  the  inexperience  of  the  mill- 
man  with   them   and  to   his  proceeding   on   the   theory   that   their 


MERCURY     TRAP. 

(Denver  Engineering  Works  Co.,  Denver,  Colo.) 

introduction  in  the  mill  is  a  reflection  on  his  ability  as  an  amalga- 
mator, as,  in  truth,  it  often  is. 

Plates  Away  from  Mortar. — The  placing  of  the  plates  at  a  distance 
from  the  mortars,  instead  of  immediately  following  them,  has  not 
been  entirely  successful.  The  first  reason  being  that  it  is  hard  to 
distribute  the  pulp  evenly  across  the  width  of  the  plates.  The 
second  is  that  the  gold  appears  to  become  coated  with  slime  in  the 
short  time  that  elapses  between  its  leaving  the  mortar  and  reaching 
the  plates,  so  that  it  is  rendered  less  amalgamable.  The  third  is 
that  the  pulp  loses  its  homogeneity  to  some  extent  in  its  passage,  just 
as  in  a  tailing  flume  the  coarse  sand  settles  to  the  bottom.  AVhen 
the  pulp  in  this  condition  reaches  the  plates,  the  coarser  sand  tends' 
to  segregate,  while  the  finer  and  more  dilute  portion  of  the  pulp 
passes  on  and  over  the  plate ;  thus  a  steeper  grade  of  plates  and 
more  water  are  required.  The  pulp  flows  down  over  the  plate  in  a 
sheet,  or  flood,  rather  than  with  the  rolling  over  and  over  wave 
motion  so  desirable,  and  amalgamation  must  necessarily  be  poor, 
especially  with  a  gold  difficult  to  catch.  The  pulp  as  it  leaves  the 
mortar  is  homogeneous,  though  the  tendency  of  the  coarse  and  fine 
particles  to  separate  is  noticeable  toward  the  foot  of  a  long  plate. 

Where  the  ore  has  been  dry-crushed  and  subsequently  watered 
and  run  over  plates,  the  results  have  been  unsatisfactory  in  many 
cases,  partly  for  the  above  reasons  and  partly  because  the  gold  has 
become  fouled,  retarding  amalgamation  by  being  coated  with  dirt 
or  air  bubbles  in  the  process  of  being  crushed. 

In  placing  plates  at  a  distance  from  the  mortars,  well  considered 
arrangements  should  be  made  for  securing  an  even  distribution  of 
pulp  to  and  across  the  width  of  them.  Comparative  tests  should 


CHARACTERISTICS  OF  AMALGAMATING  PLATES  137 

be  conducted  against  a  plate  set  in  front  of  the  mortars.  Sufficient 
mill  space  should  always  be  provided  to  allow  plates  to  be  placed 
directly  in  front  of  the  mortars,  if  thought  desirable.  With  a 
clean  ore  that  slimes  but  little  and  a  coarse  gold,  it  should  be  possi- 
ble to  amalgamate  satisfactorily  at  a  distance  from  the  mortar,  but 
with  a  sliming  ore  and  fine  gold  it  is  doubtful. 

Silvered  or  Raw  Copper  Plates  and  their  Handling. — The  apron- 
plates  may  be  of  raw  copper,  but  those  plated  with  silver  are  much 
preferred.  The  amount  of  silver  used  per  square  foot  varies  from 
1  to  3  oz.  One  ounce  is  sufficient  for  the  upper  plates,  but  the  last 
one  should  have  a  heavier  coating  as  the  scouring  action  over  it  is 
much  greater  than  above  where  more  amalgam  is  deposited.  These, 
plates  are  from  52  to  56  in.  wide — slightly  wider  than  the  discharge 
to  them — and  can  be  obtained  in  lengths  of  12  ft.,  but  are  com- 
monly used  in  sections  of  4  ft.,  and  such  a  section  is  usually  spoken 
of  as  a  plate.  The  usual  thickness  is  %  in.,  though  plates  Vie  i*1- 
thick  are  in  use,  but  such  plates  are  easily  dented  by  objects  falling 
on  them.  The  best  Lake  Superior  or  electrolytic  copper  is  used  to 
insure  purity  and  softness.  As  these  plates  are  rolled  out,  which 
makes  tho  surface  dense,  in  purchasing  raw  copper  plates  it  should 
be  stipulated  that  they  be  annealed;  the  annealing  softens  the 
surface  of  the  copper  that  the  mercury  may  be  better  absorbed. 
They  can  be  softened  by  heating  over  a  fire,  but  this,  if  not  evenly 
done,  is  liable  to  buckle  the  plate,  so  that  it  is  better  not  to  try  it, 
but  to  use  the  plate  as  it  is. 

Silver-plated  apron-plates  are  used  in  most  mills,  and  are  pre- 
ferred by  amalgamators  as  being  easier  to  care  for.  Experiments 
have  shown  that  a  greater  saving  can  be  made  with  silvered  plates 
than  with  the  raw  copper.  Still,  the  amalgamator  who  has  handled 
both  and  who  knows  how  to  care  for  the  raw  copper  plate,  believes 
that  he  can  amalgamate  as  well  with  one  as  with  the  other.  It  ap- 
pears that  the  personal  equation  of  the  amalgamator's  ability  be  . 
comes  a  greater  factor  with  raw  copper  than  with  silvered  plates. 

One  objection  to  the  use  of  raw  copper  plates  is  the  trouble 
necessary  to  get  them  into  suitable  condition.  It  requires  a  few 
weeks  before  they  become  saturated  with  mercury  and  while  'there 
is  not  a  large  amount  of  gold  carried  into  the  copper,  there  is  quite 
an  amount  on  the  surface  of  the  plate  which  it  is  not  desirable  to 
remove  as  being  prejudicial  to  the  further  good  working  of  the 
plate.  The  silvered  plate  has  a  suitable  surface  already  prepared. 
The  mercury  sinks  slowly  through  this  silvered  surface,  so  that  the 
plate  on  the  start  does  not  have  to  be  dressed  with  additional  mer- 


138  AMALGAMATING  A  RAW  COPPER  PLATE 

cury  as  often  as  the  raw  copper,  but  eventually  it  absorbs  as  much 
mercury  as  the  raw  copper  plate.  The  amount  of  gold  carried  into 
the  copper  has  been  found  to  be  small,  assays  of  plates  in  long  use 
showing  about  one-sixth  ounce  of  fine  gold  per  square  foot,  conse- 
quently the  great  amount  of  bullion  coming  from  old  plates  is  from 
the  hard  scale  of  amalgam  on  the  surface,  and  the  amalgamator 
should  aim  to  keep  this  as  small  as  possible.  It  has  been  stated  that 
microscopical  examination  has  shown  the  gold  within  the  plate 
proper  to  be  mainly  in  the  blowholes  of  the  copper,  rather  than  to 
be  truly  absorbed.  Once  a  raw  copper  plate  is  well  started  and  in 
the  hands  of  a  good  amalgamator  it  should  do  first-class  work,  but 
the  bullion  returned  for  the  first  month  in  operation  will  be  less 
than  if  a  silvered  plate  was  used.  The  difference  is  not  lost— the 
gold  is  held  on  the  surface  of  the  plate. 

To  prepare  a  raw  copper  plate  for  amalgamating,  it  is  necessary 
to  clean  the  surface  of  all  impurities  and  copper  compounds,  and  to 
a  lesser  extent,  to  soften  the  copper,  after  which  it  is  amalgamated 
by  rubbing  mercury  in.  The  cleaning  is  done  by  thorough  scrub- 
bing with  fine  sand,  wood  ashes,  or  slime,  using  wood  blocks,  rags, 
or  whisk  brooms.  Immediately  following  this  burnishing,  a  weak 
solution  of  potassium  cyanide,  sal-ammoniac,  nitric  acid,  or  caustic 
soda  or  potash  is  used  with  a  view  to  softening  the  copper.  The 
plate  can  be  amalgamated  without  any  softening  in  this  way,  but 
the  mercury  is  not  so  readily  absorbed  and  consequently  it  is  a 
longer  process.  For  this  reason  one  of  these  chemicals  is  used  in 
the  initial  process  of  amalgamating  of  a  new  raw  copper  plate,  even 
by  those  who  are  prejudiced  against  the  use  of  chemicals  on  the 
plates  under  other  conditions.  The  plate  is  usually  scrubbed  after 
the  burnishing  with  a  5%  solution  of  nitric  acid  followed  by  another 
scrubbing  with  a  2,^/2%  solution  of  potassium  or  sodium  cyanide — 
the  acid  being  washed  away  thoroughly  that  it  may  not  re-act  to 
neutralize  the  cyanide ;  the  cyanide  is  washed  away  and  followed  by 
spraying  mercury  (to  which  it  is  well  to  add  a  little  sodium  amal- 
gam) over  the  plates  and  rubbing  for  a  long  time ;  mercury  is  added 
from  time  to  time  and  the  rubbing  continued  until  the  plate  will 
hold  no  more.  With  the  passing  of  time  mercury  is  absorbed  into 
the  plate  and  the  process  of  rubbing  mercury  is  continued  until  the 
plate  is  saturated  with  mercury,  which  will  take  about  two  weeks, 
when  it  is  ready  for  the  dropping  of  the  stamps.  After  the  first 
amalgamating  no  acid  should  be  used  on  the  plates,  though  the 
cyanide  solution  may  be  used  if  the  mercury  does  not  readily  amal- 
gamate the  copper.  Following  the  first  amalgamating  or  just  before 
dropping  the  stamps,  the  plate  should  be  coated  with  silver  amalgam 


AMALGAMATING   A   SILVERED   PLATE  139 

or  the  ordinary  amalgam,  if  either  can  be  obtained ;  this  will  cause 
the  plate  to  get  into  condition  quickly  and  to  become  a  good  catcher 
of  gold  almost  from  the  start. 

Silver-plated  copper  plates  require  but  little  preparation.  They 
should  be  washed  with  a  weak  solution  of  lye  to  remove  any  grease 
on  their  surface,  and  they  may  be  polished  with  a  little  slime  or 
ashes,  though  the  latter  is  not  necessary.  A  long  and  thorough  rub- 
bing in  of  mercury  is  desirable.  Silver  amalgam  or  the  ordinary 
amalgam  should  be  applied,  if  obtainable.  If  amalgam  is  not  ap- 
plied, then  some  sodium  amalgam  should  be  added  in  the  mercury 
to  make  the  plate  more  active  at  the  start.  When  starting  new 
plates,  a  low-grade  ore  should  be  run  through  first,  preferably  one 
having  a  coarse,  easily  amalgamated  gold,  certainly  never  a  high- 
grade  ore  as  the  catching  power  of  a  new  plate  is  low.  After  a  bed 
of  amalgam  is  started,  a  better  grade  of  ore  can  be  milled. 

Recovering  Gold  from  Old  Plates. — A  much  discussed  question 
is  how  to  prevent  the  locking  up  of  a  large  amount  of  bullion  in  the 
plates.  To  melt  the  plates  into  a  bar  of  base  bullion  requires  a  new 
set  which  is  costly.  While  the  old  set  will  more  than  pay  for  the 
new,  all  would  prefer  some  way  by  which  they  could  'eat  their  cake 
and  still  have  it.'  Of  this  locked-up  gold,  comparatively  only  a 
small  part  is  absorbed  in  the  plates,  probably  1/6  or  %  oz.  of  fine 
gold  per  square  foot,  and  most  of  it  in  the  surface  copper,  as  has 
been  shown  by  planing  plates  and  assaying  the  different  sets  of 
shavings.  The  major  portion  of  the  gold  is  in  the  form  of  a  hard 
scale  of  amalgam;  to  remove  this  scale  the  copper  must  be  laid 
bare  and  will  thus  have  its  amalgamating  efficiency  reduced  for 
some  time,  which  means  a  loss.  To  resilver  the  plate  is  expensive. 
The  wet  amalgamator  attempts  to  keep  the  thickness  of  this  scale 
at  a  minimum  by  softening  the  amalgam  down  to  the  silver-plating, 
the  dry  amalgamator  accomplishes  it  by  chiseling  the  amalgam  off 
at  intervals;  but  the  scale  is  certain  to  accumulate  unless  they  are 
willing  to  ruin  the  silver-plating  and  thereby  lose  its  advantages. 
Certain  mills  use  raw  copper  plates,  with  the  exception  of  the  last 
plate  which  is  silvered  on  account  of  the  scouring  action  of  the  pulp. 
These  copper  plates  are  periodically  sweated  and  in  this  way  there 
is  little  hard  scale  left  on  the  plates.  Where  a  part  of  the  amalgam 
is  spread  back  011  the  plates,  the  practice  is  a  good  one,  but  where 
the  stamps  are  started  up  with  the  plates  bare,  it  must  be  con- 
demned. 

Where  it  is  considered  necessary  to  use  silvered  plates,  and  it 
is  still  desired  to  secure  this  bullion,  it  is  more  economical  to 


140  CYANIDE   ON   PLATES 

scale  the  plates  and  have  them  resilvered  than  to  melt  them  into 
a  bar  for  shipment  to  the  bullion  buyers.  There  is  no  really  good 
method  for  removing  this  scale.  Besides  sweating  and  chiseling, 
the  plate  can  be  given  repeated  scourings  with  pumice  stone  and 
mercury,  and  it  is  surprising  the  amount  of  gold  that  can  be  taken 
from  a  plate  in  this  way.  It  is  recommended  that  this  method  be 
followed,  and  that  in  no  case  should  the  plates  be  melted  down  where 
others  must  be  installed.  'Burning'  the  plate  is  resorted  to,  which 
consists  in  driving  off  the  mercury  by  heating  the  under  side  of  the 
plate,  after  which  the  gold  can  be  scaled  off.  To  induce  the  scale 
to  more  readily  come  off,  the  plate  being  burnt,  may  be  subjected 
to  a  scouring  with  or  a  bath  in  some  chemical  that  will  form  a 
compound  with  copper,  thereby  softening  the  surface  copper.  Burn- 
ing a  plate  causes  it  to  buckle  and  puts  it  in  such  bad  condition  that 
plates  to  be  resilvered  or  re-used  should  not  be  treated  in  that  way 
unless  the  heat  applied  is  moderate  or  there  are  facilities  for  re- 
storing the  plane  surface  to  the  plate  again.  It  would  appear  that 
a  method  could  be  devised  of  using  heavy  raw  copper  plates  and 
periodically  removing  them  and  planing  the  enriched  surface  off 
by  hand  or  machinery. 

Chemicals  and  their  Use. — As  few  chemicals  as  possible  should 
be  used  in  the  treatment  of  plates.  Their  continued  employment  is 
analogous  to  the  use  of  stimulants  by  a  man.  Apparently  beneficial, 
their  after  effects  usually  more  than  counteract  their  fancied  or 
real  temporary  advantages.  The  mercury  should  be  'pickled'  in 
weak  nitric  acid  to  remove  impurities,  as  has  been  explained  before, 
but  all  traces  of  the  acid  should  be  washed  out  before  applying  the 
mercury  to  the  plates.  Greasy  plates  should  be  scrubbed  with  soap 
and  water  or  a  very  weak  solution  of  lye,  which  will  dissolve  and 
remove  the  grease.  Potassium  cyanide  has  been  used  extensively  in 
the  past,  but  its  use  must  be  condemned  as  wrong  in  theory  and 
harmful  in  results.  Cyanide  of  potassium  solution  removes  grease, 
in  which  it  is  beneficial ;  it  also  dissolves  the  compounds  of  copper, 
allowing  them  to  be  washed  away,  in  which  it  is  also  beneficial ;  but 
it  goes  farther,  it  dissolves  the  metallic  copper  itself  and  thereby 
pits  the  surface  of  the  plate,  especially  if  the  coating  of  amalgam  is 
thin.  This  pitting  of  the  plate  and  the  formation  of  compounds  of 
copper  and  cyanide  that  are  only  partly  removed  by  the  water,  in- 
creases the  tendency  of  the  plate  to  absorb  mercury — is  said  to 
soften  the  plate.  But  these  beneficent  results  are  only  temporary, 
for  the  plate  becomes  still  harder  and  the  mercury  tends  to  ooze 
out  of  the  amalgamated  plate,  as  may  be  observed  in  plates  that  have 


SODIUM   AMALGAM  141 

been  continually  treated  with  strong  cyanide  solution,  while  the 
copper  compounds  that  have  been  formed,  oxidize  to  tarnish  the 
plate  at  every  opportunity.  When  the  solution  is  used,  it  should  be 
weak,  that  only  the  copper  compounds  may  be  attacked,  and  that 
the  raw  copper  may  be  unacted  upon,  and  it  should  be  thoroughly 
washed  away  immediately  after  using,  that  none  of  the  copper  com- 
pounds or  salts  may  remain.  A  2*/>>%  solution — less  than  one-half 
ounce  potassium  cyanide  to  a  pint  of  water — is  the  strength  generally 
used,  and  a  still  weaker  solution  is  preferable.  Plates  that  have 
been  long  treated  with  strong  cyanide  solution  are  difficult  to  han- 
dle, especially  if  little  amalgam  is  kept  on  them,  and  that  in  a  hard 
condition.  In  general,  any  acid  or  chemical  that  will  form  a  com- 
pound with  copper  should  not  be  applied  to  the  plates,  while  the 
copper  should  be  kept  well  covered  with  amalgam  that  tarnishing 
due  to  oxidation  by  the  air  or  indirectly  by  the  acidity  of  the  water 
or  ore  may  be  minimized. 

Amalgamators  have  various  'dopes'  and  nostrums,  secret  and 
otherwise,  for  applying  to  the  mercury  and  plates,  the  action  of 
which  they  themselves  but  little  understand,  especially  in  regard  to 
the  chemical  reactions  from  which  they  must  derive  their  virtue,  if 
they  possess  any.  It  is  best  to  dispense  with  them  all.  There  is  only 
one  'dope'  or  panacea  for  the  ills  of  amalgamation,  and  that  is  a 
thick  bed  of  amalgam,  kept  in  an  active  condition  and  free  from 
foreign  substances.  This,  together  with  a  vigorous  application  of 
'elbow  grease,'  produces  the  best  results. 

The  mercury  is  sometimes  'loaded'  by  adding  sodium  amalgam, 
up  to  the  point  where  the  mercury  just  commences  to  amalgamate 
a  bright  or  newly  filed  nail.  Sodium  amalgam  is  prepared  by  heat- 
ing the  mercury  in  a  glazed  dish,  or  better  still,  a  quicksilver  flask, 
the  top  of  which  has  been  cut  off  to  form  a  deep  pot.  The  making 
of  sodium  amalgam  is  attended  with  danger  and  should  be  conducted 
carefully.  Heat  the  mercury  to  about  300°F.  (149°C.)  and  cut  small 
chips,  the  size  of  a  good-size  pea,  from  the  stick  of  sodium,  han- 
dling with  a  pair  of  tongs.  Drop  but  one  chip  into  the  heated  mer- 
cury at  a  time.  A  slight  explosion  should  follow.  If  it  does  not,  stir 
it  gently  with  a  wooden  paddle,  which  will  hasten  the  flash.  Then 
add  another  chip  in  like  manner,  up  to  3%  of  the  weight  of  the  mer- 
cury to  be  thus  treated.  This  will  crystallize,  forming  a  solid  amal- 
gam when  cold.  Keep  the  face  away  from  the  flask,  both  on  account 
of  the  flashing  sodium  and  to  avoid  the  mercurial  vapor  that  is 
likely  to  arise  from  the  heated  pot.  This  amalgam  should  be  kept 
in  air-tight  bottles  that  it  may  not  decompose,  and  should  be  added 


142  SILVER   AMALGAM 

in  small  quantity  to  the  mercury  as  required.  The  effect  of  the 
sodium  in  making  the  mercury  so  active  in  amalgamating  is  not 
fully  understood,  but  is  supposed  to  be  largely  due  to  its  reducing 
action.  It  reduces  the  oxides  and  other  compounds  of  the  base 
metals,  causing  them  to  amalgamate  with  the  mercury.  It  is  but 
little  used  by  practical  amalgamators  as  it  causes  the  amalgam  to 
'freeze'  to  the  iron  and  steel  surfaces  of  the  mortar  through  amal- 
gamating with  them,  while  so  much  fine  iron  and  steel  and  sulphide 
are  caught  with  the  plate  amalgam,  that  these  surfaces  become  foul. 
It  is  productive  of  an  increased  quantity,  but  a  lower  grade  of 
amalgam.  Besides  being  useful  in  covering  bare  spots,  it  is  of 
benefit  in  starting  new  plates — making  them  more  active. 

Silver  amalgam  can  be  prepared  by  dissolving  silver  coin  or  other 
silver  in  dilute  nitric  acid.  To  this  solution  add  the  mercury  and  a 
few  bright  nails,  keeping  the  acid  weak.  The  silver  will  be  deposited 
on  the  mercury  forming  an  amalgam.  Unless  the  amount  of  copper 
in  the  silver  is  large,  its  presence  is  not  material.  This  copper  can 
be  removed  by  precipitating  the  silver  from  the  nitrate  solution  by 
adding  a  solution  of  common  salt  up  to  the  point  where  no  more 
precipitation  occurs,  then  washing  the  precipitate  until  all  green 
color  of  copper  is  gone,  after  which  very  dilute  nitric  or  sulphuric 
acid,  mercury,  and  bright  nails  are  added.  The  finely  divided 
precipitated  silver  may  be  separated  by  filtering,  and  worked  up 
with  the  mercury  later,  if  that  method  is  preferred.  A  rough  method 
of  making  silver  amalgam  is  to  reduce  the  silver  to  filings  and 
amalgamate  it  by  mixing  with  mercury. 

Unsatisfactory  Bare  and  Hard  Plates. — The  stains,  the  so-called 
'verdigris,'  which  appear  on  the  plates  very  much  resembling  bare, 
spots  and  which  are  a  source  of  grief  to  many  amalgamators,  are 
in  nearly  every  case  an  oxide  of  copper,  though  they  may  be  a 
carbonate  in  some  instances.  These  stains  are  due  to  copper  in  the 
amalgam,  which  is  turned  into  an  oxidized  compound  by  the  air  or 
water.  This  copper  may  be  amalgamated  from  the  ore  together  with 
the  gold,  or  may  have  its  source  in  the  shells  of  detonators  used  in 
blasting,  or  may  have  contaminated  the  mercury.  Another  cause 
of  the  stains  is  acidity  in  the  battery-water  or  ore,  which  may  arise 
from  decomposing  sulphides  producing  sulphuric  acid,  which  in  turn 
acts  upon  the  copper  of  the  plate,  forming  the  compound  which  is 
the  stain.  Generally  the  stains  arise  from  the  plate  due  to  too  thin 
a  film  of  amalgam,  and  to  the  overuse  of  chemicals.  The  remedy  is 
to  use  purified  mercury,  and  dress  the  plates  as  often  as  the  stains 
appear  until  a  good  film  of  amalgam  is  accumulated  over. the  plate, 


STAINS  AND  BARE  SPOTS  ON  PLATES  143 

and  especially  over  the  spots  which  most  frequently  tarnish.  Solu- 
tions of  potassium  cyanide,  sal-ammoniac,  and  of  the  acids  are  used, 
especially  the  first,  to  dissolve  these  stains  that  they  may  be  washed 
away,  but  as  it  is  impossible  to  prevent  the  chemicals  from  con- 
tinuing to  act  further,  they  should  not  be  employed.  The  use  of 
silvered  instead  of  raw  copper  plates  will  ordinarily  obviate  this 
trouble.  However,  it  largely  depends  upon  the  ability  of  the  amalga- 
mator. 

Bare  spots  on  the  plates  are  due  to  the  amalgam  having  been  re- 
moved too  close  to  the  copper  by  chiseling,  or  they  may  be  started 
by  a  tarnishing  spot.  They  also  may  appear  on  the  lower  apron-plate 


IRON     HANI)     MORTAR     FOR     GRINDING  WEOGEWOOD     BOWL     FOR     GRINDING 

AMALGAM.  AMALGAM. 

(Braun-Knecht-Heimann  Co.,  San  Francisco.) 

due  to  the  scouring  of  the  pulp  as  has  been  mentioned  before.  These 
spots  require  careful  treatment  for  a  little  while.  The  copper  should 
be  burnished  with  fine  grit,  such  as  wood  ashes  or  slime,  until  the 
pure  copper  is  exposed,  when  the  adjacent  amalgam  should  be 
worked  over  it  and  well  rubbed  in.  The  deposition  of  the  amalgam 
should  be  coaxed  from  the  edges  to  the  center.  A  little  sodium  can 
be  used  to  advantage  in  the  mercury  and  this  compound,  sodium 
amalgam,  applied  to  these  spots,  as  it  will  promote  the  attachment 
between  the  amalgam  and  the  plate  and  aid  in  the  recovery  of 
additional  amalgam.  Cyanide  and  acid  solutions  should  not  be  used 
on  these  spots. 

Some  amalgamators  are  troubled  by  the  amalgam  on  the.  apron- 
plates  becoming  abnormally  hard.  The  exact  reason  for  this  cannot 
be  given,  though  it  is  often  due  to  certain  substances  in  the  ore,  but 
usually  it  is  the  combination  of  a  bare  plate,  dry  amalgamation,  and 
the  too  frequent  use  of  cyanide  in  dressing  the  plates.  The  amalga- 
mator, in  his  effort  to  prevent  this  hardening  of  the  plate,  may  dress 
it  wet  until  it  resembles  a  mirror,  but  in  a  short  time  the  mercury 
begins  to  form  in  visible  globules  and  drain  off,  leaving  the  plate 


144 


CORRECTING   HARD   PLATES 


hard.  To  correct  this  trouble  all  chemicals  should  be  dispensed 
with,  and  the  principles  of  wet  amalgamation  practised  by  keeping 
a  thick  layer  of  amalgam  on  the  plates  and  dressing  them  often, 
giving  the  amalgam  a  long  and  hard  rubbing.  This  amalgam  should 
not  be  kept  too  wet  or  it  will  increase  the  tendency  for  the  plate  to 
'run.'  Unless  the  trouble  lies  in  the  ore  or  water,  the  plate  will  re- 
gain its  normal  condition  under  this  treatment. 

Cleaning  Amalgam  and  the  Clean-Up. — After  the  amalgam  is  re- 
moved at  the  daily  cleaning  of  the  plates,  it  is  necessary  to  clean 
it  by  removing  the  sand,  iron,  sulphide,  and  base  metal  dross.  This 
is  done  by  grinding  it  in  a  wedgewood  or  iron  bowl  with  enough 


AMALGAM 

The  amalgam  is  placed  in  a  canvas  bag  and  inserted  in  the  perforated 
cylinder  that  the  ram  may  descend  upon  it. 

(Power  &  Mining  Machinery  Co.,  Cudahy,  Wis.) 


mercury  to  make  it  quite  liquid.  The  impurities  rise  to  the  top, 
where  they  are  carried  over  the  side  of  the  bowl  into  a  gold  pan  in 
which  the  bowl  sets,  by  a  stream  of  water  from  a  hose,  or  they  are 
taken  off  by  a  coarse  sponge.  After  the  quartz  and  dirt  and  dross — 
impure  and  foul  amalgam — has  been  taken  off,  a  magnet  is  passed 
through  the  liquid  amalgam  several  times  to  remove  the  fine  iron  and 
steel.  It  is  now  poured  into  a  wet  canvas  or  a  double  thickness  of 


SQUEEZING   AMALGAM  145 

stout  drilling  lining  a  bowl.  The  cloth  is  gathered  up  by  the  corners 
and  twisted  tight,  forcing  the  liquid  mercury  through  the  fabric  and 
leaving  the  hard  amalgam  behind  in  the  cloth.  This  process  of 
squeezing  or  wringing  the  amalgam  is  continued,  the  globules  of 
mercury  being  washed  off  by  aid  of  water  into  the  bowl  beneath. 
When  all  the  mercury  has  been  expressed  that  th.e  operator  can 
wring  from  it,  the  cloth  is  spread  out  exposing  a  ball  of  hard  amal- 
gam within.  The  ball  is  rolled  around  in  the  cloth  to  pick  up  the, 
loose  flakes  of  amalgam;  after  which  the  ball  is  weighed,  wrapped 
in  paper  on  which  is  usually  marked  the  date  and  weight,  and  locked 
up  until  the  monthly  or  semi-monthly  retorting  and  melting.  The 
mercury  passing  through  the  cloth  will  carry  some  gold,  but  this 
is  not  considered  undesirable  as  such  mercury  is  more  active  in 
promoting  amalgamation  than  that  which  is  gold-free.  The  amount 
of  gold  so  retained  can  be  reduced  by  squeezing  the  amalgam  through 
a  less  porous  material,  such  as  chamois.  Mechanical  amalgam 
squeezers  are  in  use.  Their  product  is  not  as  satisfactory  as  that 
produced  by  hand,  but  as  they  work  faster  and  save  labor  they  are 
suitable  where  a  large  amount  of  amalgam  is  produced.  Where 
compressed  air,  steam,  or  water  pressure  is  available  at  the  mill, 
they  can  be  rigged  up  out  of  an  old  air  rock  drill. 

Some  amalgamators  clean  the  amalgam  by  adding  sufficient  mer- 
cury to  make  it  soft  and  mushy,  when  it  is  dumped  upon  the  upper 
apron-plate,  where  it  is  puddled  by  the  fingers,  or  a  rubber,  until  it 
sticks  to  the  plate  in  one  mass.  Water  is  turned  on  from  a  hose, 
which,  in  connection  with  the  puddling,  washes  the  amalgam  clean. 
After  using  the  magnet,  the  amalgam  is  scooped  up  and  transferred 
to  the  straining  cloth.  This  is  a  poor  method,  though  the  amount 


GOLD    PAN    WITH    BOTTOM    OF    COPPER    FOE    AMALGAMATION    PURPOSES. 

(Braun-Knecht-Heimann  Co.,  San  Francisco.) 

of  amalgam  lost  is  small  when  the  treasure  box  is  used;  it  causes  a 
loss  of  running  time  and  leaves  a  wet  spot  on  the  plate.  The  easiest 
way  is  to  use  a  gold  pan  having  an  amalgamated  copper  bottom  on 
the  inside,  when  removing  the  amalgam  from  the  plates.  Then, 
when  at  leisure,  work  this  amalgam  up  at  the  clean-up  sink  in  the 
same  manner  as  on  an  apron-plate.  Grinding  with  an  excess  of  mer- 
cury in  a  wedgewood  bowl  gives  the  cleanest  amalgam.  The  dross 
or  impure  mercury  and  the  rich  sulphide  collecting  from  the  daily 


146 


BATTERY    CLEAN-UP 


cleaning  of  the  amalgam  should  be  ground  with  mercury  when  a 
quantity  has  collected.  All  of  the  debris  and  refuse  from  these  clean- 
ings should  finally  go  to  the  tank  of  the  clean-up  sink,  to  be  run 
through  the  clean-up  barrel  or  pan  later,  or  sent  through  the  mortars 
in  the  absence  of  a  clean-up  barrel  or  pan. 

Where  there  is  considerable  gold  in  the  mortar  sand,  this  sand 
is  removed  once  a  month  or  on  a  general  clean-up  day.    At  this  time 


CLEAN-UP   BARBEL. 

(Power  &  Mining  Machinery  Co.,  Cudahy,  Wis.) 


the  battery  is  stamped  out  and  hung  up.  The  apron-plates  are 
cleaned  before  the  mortar  is  opened.  A  platform  of  boards  with 
cleats  to  fit  the  apron-table  is  placed  over  the  first  plate  to  work 
upon  without  marring  the  plate.  The  screen  is  removed.  The  splash, 
lip,  and  inside  plates  are  removed  to  the  clean-up  room  to  be  chiseled 
and  scraped,  which  is  done  by  means  of  old  files  forged  down  to 
chisel  ends  and  ground  sharp  on  a  grindstone  or  emery  wheel.  A 
putty  knife  is  a  useful  tool  for  this  purpose.  The  pulp  lying  on  the 
dies  is  shoveled  into  boxes  or  tubs  to  be  returned  to  the  mortar,  as 
it  usually  contains  too  little  amalgam  to  be  treated.  The  sand  about 
the  dies  is  dug  out  with  small  bars  and,  together  with  that  under- 


BATTERY   CLEAN-UP  147 

neath  the  dies,  is  carried  in  pails  or  tubs  to  the  clean-up  room,  or 
to  the  clean-up  barrel  or  pan.  The  dies  are  pried  up  and  removed 
to  get  the  amalgam-bearing  sand  around  and  beneath  them.  All  the 
sand  is  removed,  together  with  any  amalgam  adhering  to  the  sides 
of  the  mortar  or  to  the  shoes  and  bosses.  The  dies,  which  have  been 


STAMP-MILL    BATEA. 

(Joshua  Hendy  Iron  Works,  San  Francisco.) 

washed  and  examined  for  any  deposits  of  amalgam,  are  returned  to 
the  mortar.  The  height  of  drop  is  adjusted.  The  chuck-block, 
screen,  and  plates  are  put  in  position,  and  the  battery  started  up. 
It  is  aimed  to  put  the  new  shoes  and  dies  in  at  this  time  whenever 
possible,  and  the  mercury  traps  are  also  then  cleaned.  Where  the 
amount  of  gold  retained  in  the  mortar  sand  is  too  small  to  make 
it  advisable  to  lose  the  running  time  and  the  labor  necessary  to  ob- 
tain it,  the  clean-up  will  consist  in  scraping  the  outside  and  inside 
mortar-plates  and  perhaps  the  apron-plate  also;  the  battery  sand 
being  removed  and  treated  only  when  new  dies  are  put  in.  At  some 
mills  the  battery  sand  from  all  the  mortars,  when  low  in  amalgam, 
is  sent  through  one  mortar  having  a  high  discharge,  and  only  the 
sand  from  this  mortar  is  taken  to  the  clean-up  room,  but  it  is  not  con- 
sidered good  practice.  At  the  clean-up  room  the  sand  from  the 
mortars  is  either  panned  down  in  an  ordinary  gold  pan  or  is  run 


148 


CLEAN-UP   BARREL 


through  a  rocker  to  separate  and  collect  the  amalgam,  the  sand  tail- 
ing being  fed  through  the  mortar  before  the  next  clean-up. 

If  a  clean-up  barrel  is  used,  the  mortar  and  mercury-trap  sands, 
together  with  that  in  the  clean-up  sink  from  the  daily  cleaning  of 
the  amalgam,  are  put  in  the  barrel  with  40  Ib.  or  more  of  mercury— 
sufficient  to  insure  the  amalgam  being  liquid — also  enough  water  to 
make  a  sludge  or  thick  pulp.  To  this  is  added  a  little  lye,  usually 


CLEAN-UP   PAN. 

(Traylor  Engineering  &  Manufacturing  Co.,  Allentown,  Pa.) 

one  small  can,  to  'cut'  the  grease  and  keep  the  mercury  in  condition; 
also  many  pieces  of  iron  and  steel  to  act  as  grinders  or  mullers,  such 
as  cannon  balls,  broken  stem-ends,  and  shoe-shanks.  Pieces  of  hard 
quartz  or  other  rock  answer  well.  The  barrel  is  now  revolved  from 
three  to  eight  hours,  depending  on  the  ideas  of  the  amalgamator  and 
the  time  available,  at  a  speed  not  exceeding  fifteen  revolutions  per 
minute — the  higher  the  speed,  the  greater  the  tendency  of  the  amal- 
gam to  flour.  After  grinding,  the  barrel  is  slowed  down  in  order 


STAMP-MILL   BATEA  149 

that  the  soft,  liquid  amalgam  may  collect ;  it  is  finally  stopped  with 
the  manhole  uppermost  and  a  small  plugged  opening  below.  The 
manhole  is  opened  first  to  give  vent  to  any  gases  that  may  have 
formed,  after  which  the  plug  below  is  removed  to  allow  the  amalgam 
to  run  into  a  deep  receptacle  or  pail  set  underneath.  The  sand  is 
slowly  sluiced  out  of  the  barrel  with  sufficient  water  to  make  a  thin 
pulp  that  will  not  carry  away  any  amalgam  as  it  overflows  the  pail. 
It  is  run  through  a  coarse  screen  to  remove  nails  and  other  small 
fragments  of  iron,  to  riffles  and  an  amalgamated  plate  for  catching 
any  escaped  amalgam,  and  is  finally  caught  in  a  box  or  tank.  A 
stamp-mill  batea,  a  large  shallow  iron  bowl  or  pan  which  may  be 
characterized  as  a  mechanically-operated  gold  pan  that  retains  the 
amalgam  and  pans  off  the  sand,  is  superior  to  riffles  or  a  plate  for 
catching  any  amalgam  that  has  overflowed  the  pail.  The  amalgam 
recovered  is  cleaned  of  iron  by  the  magnet  and  strained  through 
canvas  into  balls  in  the  usual  manner.  The  sand  is  eventually  car- 
ried back  to  the  mortar  as  it  always  contains  a  little  amalgam. 
Grinding  pans  are  used  at  some  mills  instead  of  barrels  for  cleaning 
the  sand  and  amalgam ;  the  only  variation  in  the  general  treatment 
being  that  necessitated  by  the  difference  in  their  construction ;  both 
are  dispensed  with  at  many  mills  as  they  are  considered  by  some  to 
flour  the  amalgam,  while  on  the  other  hand  some  mills  are  equipped 
with  both.  The  amalgam  chiseled  from  the  plates,  or  that  panned 
out  of  the  sand,  is  ground  up  in  a  large  wedgewood  bowl  or  in  an 
iron  hand-mortar  with  an  excess  of  mercury.  Warm  water  is  often 
used  in  cleaning  the  amalgam  that  it  may  become  softer  and  liberate 
more  freely  the  impurities  mechanically  held  or  suspended  in  it, 
and  that  it  may  be  squeezed  drier.  Some  amalgamators,  though  not 
many,  add  the  amalgam  chiseled  from  the  plates  at  the  clean-up  to 
the  sand  in  the  barrel  and  clean  it  in  that  way,  but  it  is  not  good 
practice  to  thus  take  any  chances  of  its  being  lost  or  stolen. 


CHAPTER  VIII 

RETORTING  AND  PERCENTAGE  OF  METAL  IN  AMALGAM — MELTING  AND 
SAMPLING  BULLION  — •  RECOVERING  GOLD  FROM  SLAG,  OLD 
SCREENS,  ETC. 

Retorting  and  Percentage  of  Metal  in  Amalgam. — The  amalgam  is 
retorte  I  to  free  the  gold  from  the  mercury.  This  is  accomplished  in 
a  closed  cast-iron  vessel  having  a  tube  leading  from  it  to  carry  away 
the  volatilized  mercury  and  deliver  it  to  a  kettle  re-condensed  in 
liquid  form.  These  vessels  are  called  retorts,  and  may  be  either  large 
cylinders  solidly  set  in  a  foundation  of  brick  over  a  fire-box,  or  they 
may  be  small  portable  affairs  that  are  placed  over  a  fire  made  in  a 
temporary  furnace  of  brick  or  stone,  or  even  on  the  ground  in  the 
open  air.  The  inside  of  the  retort  is  lined  with  three  or  four  thick- 
nesses of  paper,  with  chalk,  or  with  a  paste  of  wood  ashes,  lime,  or 
red  oxide  of  iron,  to  prevent  the  gold  from  sticking  to  the  sides.  In 
the  retort  the  balls  of  amalgam  are  placed  so  that  it  will  not  be  more 
than  three-quarters  full  when  the  cover  is  placed  on.  If  the  'sponge,' 
as  the  metal  after  retorting  is  called,  is  to  be  shipped  without  being 
melted  into  a  bar,  the  amalgam  is  packed  down  tight  to  make  a  solid 
mass  of  it,  and  a  hole  is  forced  down  through  the  center  to  enable  the 
mercury  the  better  to  escape  from  within  the  mass.  If  the  retorted 
metal  is  to  be  melted  into  a  brick  before  shipping,  the  balls  are  put 
in  loosely  since  that  will  allow  the  volatilized  mercury  to  readily 
escape  and  the  sponge  to  be  easily  broken  up  for  convenience  in 
handling  in  the  melting.  A  ring  of  lute  made  of  fire-clay,  wood 
ashes,  and  a  little  salt  is  placed  between  the  cover  and  body  of  the 
retort  to  insure  an  airtight  joint.  The  retort  is  set  in  a  furnace,  on 
a  tripod,  or  is  carefully  propped  up  in  the  open,  and  a  slow  wood  fire 
started  about  it.  This  fire  is  gradually  raised  until  the  retort  finally 
becomes  cherry  red ;  the  heat  being  applied  all  about  the  retort,  not 
on  the  bottom  alone.  The  pipe  coming  out  of  the  retort  passes 
through  an  outer  pipe,  and  in  the  space  between  them  cold  water  is 
constantly  circulating,  which  condenses  the  volatilized  mercury  to 
the  liquid  state.  When  using  small  retorts,  gunnysacks  wrapped 
about  the  pipe,  to  which  cold  water  is  continually  applied,  may  suc- 
cessfully be  used.  A  vessel  filled  with  water  is  placed  at  the  lower 
end  of  the  pipe  to  catch  the  condensed  mercury.  A  cloth  should  be 
wrapped  about  the  end  of  the  tube,  forming  an  extension  of  it.  This 

150 


RETORTING 


151 


extension  should  dip  beneath  the  surface  of  the  water  with  which  the 
pail  is  filled  and  which  overflows  as  the  mercury  condenses.  Care 
should  be  taken  that  the  lower  end  of  the  pipe  itself  does  not  project 
into  the  water,  as  there  is  a  tendency  for  the  atmospheric  pressure 
to  force  the  water  up  into  the  pipe  at  times,  due  to  the  diminution 
of  the  volume  of  gas  hrthe  retort  caused  by  the  fire  being  checked 
or  dying  down ;  in  such  case  the  cloth  will  be  drawn  against  the  pipe 


BETORT   AND    CONDENSER. 

(Braun-Knecht-Heimann  Co.,  San  Francisco.) 


and  air  drawn  through  the  pores  of  the  cloth,  whereas,  if  the  end  of 
the  pipe  were  in  the  water,  the  water  might  ascend  into  the  retort 
and  an  explosion  result.  If  the  end  of  the  pipe  were  exposed  without 
the  cloth,  some  volatilized  mercury  might  escape  if  the  condenser  was 
not  working  properly,  endangering  salivation. 

Retorting  will  take  from  2%  to  5  hours.  The  fire  should  be  con- 
'  tinued  for  20  minutes  after  the  mercury  ceases  to  condense  in  the 
pipe  as  ascertained  by  tapping  the  pipe  and  watching  for  the  mercury 
to  drop  out.  When  distillation  is  complete  the  fire  is  withdrawn  and 
the  retort  allowed  to  cool.  There  is  always  danger  of  salivation  if 
the  retort  is  opened  while  hot.  It  is  practically  impossible  to  drive 
off  the  last  of  the  mercury  and  it  should  not  be  attempted  by  raising 
the  heat,  as  such  heat  may  result  in  a  partial  fusion  of  the  gold, 
causing  it  to  stick  to  the  retort,  and  is  also  destructive  of  the  retort. 
Retorting  with  an  assay  furnace  or  on  a  blacksmith 's  forge  invaria- 
bly results  in  using  too  high  a  heat.  Where  the  amount  of  amalgam 
to  be  retorted  is  large,  the  oval  or  cylindrical  retorts  of  large 


152  PERCENTAGE   OP    METAL   IN    AMALGAM 

capacity  before  referred  to  are  used  in  specially  built  furnaces. 
The  amalgam  is  placed  in  cast-iron  trays  or  separated  by  partitions 
of  plate  iron  in  these  retorts,  these  trays  or  plates  being  well  chalked 
or  painted  with  ashes,  lime,  or  other  mixture  and  well  dried  to  pre- 
vent the  gold  from  sticking  to  them. 

If  the  amalgam  has  been  properly  cleaned  and  retorted,  the  sponge 
will  show  a  gold  color  and  require  a  minimum  amount  of  flux  in 
the  melting.  Blackness  indicates  that  the  amalgam  was  poorly 
cleaned.  A  pale  whitish  color  shows  that  it  still  contains  mercury, 
and  a  bluish  color  generally  indicates  the  presence  of  lead,  usually 
babbitt.  Retorting  should  be  done  in  the  open,  or  with  the  windows 
of  the  retort  room  open,  to  lessen  the  danger  of  being  salivated, 
though  there  is  little  danger  if  proper  precautions  are  taken. 

The  percentage  of  metal  that  is  obtained  from  the  amalgam  by 
retorting  and  melting  it  into  a  bar  depends  upon  the  amount  of  im- 
purities in  the  amalgam,  and  to  a  much  greater  extent  on  the  size 
of  the  particles  of  gold.  Coarse  gold  does  not  require  as  much  mer- 
cury to  amalgamate,  or  cement  it,  as  a  fine-grained  gold.  About 
30  to  40%  is  the  usual  amount  of  bullion  obtained  from  the  amalgam 
of  ordinary  gold.  With  coarse  gold  as  high  as  65%  of  bullion  has 
been  obtained,  while  with  an  extremely  fine  gold  the  amalgam  may 
run  as  low  as  20%  of  bullion.  This  principle  is  true  with  respect 
to  the  point  at  which  the  gold  is  caught  in  the  amalgamation  process. 
The  amalgam  taken  from  the  mortar-sand  will  retort  the  highest 
percentage  of  gold,  since  only  coarse  gold  is  caught  there.  The 
amalgam  from  the  foot  of  the  table  will  retort  the  lowest  percentage 
of  gold,  as  only  very  fine  gold  will  reach  that  point  before  being 
caught.  Harder  squeezing  in  the  canvas  does  not  materially  lessen 
the  amount  of  mercury.  The  use  of  sodium  amalgam  will  increase 
the  amount  of  amalgam  by  amalgamating  the  fine  iron,  steel,  and 
sulphide.  In  one  case,  with  a  fine  gold  that  ordinarily  retorted  22% 
bullion,  sodium  amalgam  was  used  in  starting  new  plates,  resulting 
in  an  increased  yield  from  these  plates  that  assayed  only  12%  fine 
bullion. 

Melting  and  Sampling  Bullion. — Before  melting  the  retorted 
metal,  the  black-lead  or  graphite  crucible  must  be  annealed  by  driv- 
ing off  all  the  contained  moisture,  or  the  sudden  heating  of  this 
moisture  through  its  expansion  and  the  formation  of  steam  will 
burst  the  pot.  For  this  purpose  the  pot  is  kept  in  a  warm  place, 
such  as  under  or  over  a  stove  or  boiler  for  a  week  or  more,  when  it 
is  placed  directly  in  the  stove  or  in  the  boiler  fire  for  some  time, 
being  in  this  way  slowly  and  gradually  brought  to  a  very  high  heat, 


CARE   OF    CRUCIBLES  153 

after  which  it  can  be  used  with  safety.  Between  melts  the  crucible 
should  be  kept  in  a  dry,  hot  place,  for  when  below  250°F.  the  cruci- 
ble tends  to  absorb  moisture,  and  its  life  is  largely  dependent  upon 
the  thoroughly  annealed  condition  in  which  it  is  used.  The  pot  is 
placed  in  the  furnace  fire  and  when  sufficiently  heated  to  melt  the 
metal,  the  flux  is  added.  After  the  flux  has  become  molten,  the  re- 


GRAPHITE   CRUCIBLES   WITH   PINHOLE  DUE  TO   POOR   ANNEALING,   OR  CRACKED   OR 
BURST   FROM   FAILURE   TO   ANNEAL. 

(Joseph  Dixon  Crucible  Co.,  Jersey  City,  N.  J.) 

torted  metal  sponge  is  added  in  pieces  as  fast  as  it  melts  down  until 
the  whole  is  melted,  employing  a  long  scoop  or  tongs  in  handling 
the  pieces  of  gold  sponge.  The  quantity  of  the  flux  and  its  character 
will  depend  upon  the  cleanness  of  the  sponge  after  retorting  and 
the  nature  of  the  impurities.  The  amount  of  flux  used  and  the 
proportions  vary  with  each  melter  and  can  be  determined  only  in 
an  empirical  way — by  knowing  the  theory  of  fluxing  and  then  judg- 
ing the  amount  and  character  of  the  impurities.  Should  the  amount 
of  flux  appear  too  small,  as  melting  proceeds,  more  can  be  added 
at  any  time,  while  an  excess  does  no  harm,  nitre  excepted.  The 
pot  should  be  provided  with  a  cover  which  is  kept  in  place  during 
melting,  except  when  removed  for  observation  or  for  stirring  the 
melt. 

The  experienced  melter  on  a  clean  retorted  metal  will  use  little  or 
no  flux,  while  the  novice  may  use,  on  a  somewhat  base  retort,  flux 
to  the  amount  of  5  or  10%  of  the  metal.  The  average  melter  em- 
ploys borax-glass  and  bi-carbonate  of  soda  in  approximately  equal 
proportions  by  bulk.  The  professional  meltaT  confines  himself 


154  FLUXES   AND   SLAGS 

largely  to  borax-glass.  The  principal  impurities  to  be  fluxed  off  are 
oxide  of  iron,  sand,  and  a  little  sulphur.  Borax  dissolves  the  metal- 
lic oxides  forming  borates  of  the  bases ;  soda  acts  as  a  desulphurizer 
and  forms  sodium  silicates  with  the  sand ;  together  they  slag  off  the 
impurities  and  cause  the  metal  to  melt  down  rapidly.  It  is  prefer- 
able to  use  an  excess  of  borax-glass.  For  taking  care  of  small  or 
medium  amounts  of  iron,  in  addition  to  the  use  of  borax,  silica  may 
be  used  to  form  an  iron  silicate.  Where  the  retorted  metal  contains 
a  large  amount  of  iron,  sulphur  should  be  added  to  the  surface  of  the 
molten  metal  at  the  sides  of  the  melting  pot,  and  stirred  in  with  a 
plumbago  stirrer  to  form  a  matte  of  sulphide  of  iron. 

Should  the  amalgam  have  contained  some  sulphide,  the  molten 
metal  should  be  'poled'  by  allowing  a  heated  iron  rod  to  remain  in 
the  pot  for  a  little  time  to  slag  off  the  sulphur  as  iron-matte  (iron- 
sulphide).  If  the  amalgam  contained  much  metallic  iron  this  'pol- 
ing' will  not  be  required.  If  the  quantity  of  iron  sulphide  formed  is 
small,  it  will  be  dissolved  by  an  excess  of  slag;  if  large  it  will  form 
a  matte  between  the  bullion  and  slag.  This  matte  should  be  saved 
and  after  a  quantity  from  several  melts  is  collected,  should  be 
fused  with  borax  and  soda  to  form  a  button  of  gold  and  a  bar  of 
clean  matte,  or  should  be  cast  into  a  bar  and  shipped. 

Nitre  (potassium-nitrate)  is  used  to  oxidize  the  base  metals  that 
they  may  pass  into  the  slag,  but  it  also  oxidizes  the  carbon  of  the 
crucible  while  its  base — potassium — combines  or  slags  with  the  clay 
used  in  the  manufacture  of  the  crucible,  corroding  it  badly,  conse- 
quently nitre  should  only  be  used  by  the  experienced  melter.  Silica 
tends  to  increase  the  grade  of  the  bullion,  but  if  not  used  in  the  right 
proportion  the  slag  is  liable  to  become  viscous  and  contain  shots  of 
gold.  An  excess  of  soda  makes  a  liquid  slag  and  one  that  separates 
easily  from  the  bar;  a  large  excess  can  easily  be  detected  in  cold 
slag,  especially  when  slacked  or  chilled  in  water,  from  having  the 
characteristics  of  soda.  An  excess  of  soda  will  attack  the  crucible 
while  an  excess  of  borax  will  not. 

A  silicious  slag — one  containing  an  excess  of  silica — is  stringy, 
can  be  pulled  into  long  strings  when  cooling,  and  is  glassy  and 
brittle  when  cold.  When  the  slag  contains  such  an  excess  of  silica 
that  it  becomes  thick  and  viscous — it  will  still  be  stringy — it  should 
be  thinned  by  the  addition  of  soda  to  unite  with  the  silica  as  a 
sodium  silicate.  A  basic  slag — one  containing  less  than  a  normal 
amount  of  silica  or  acid  flux — is  'short,'  cannot  be  pulled  into  strings 
when  melted  or  cooling,  and  is  dull  and  stony  looking  when  cold. 
The  slag  made  in  melting  retort  metal  is  usually  of  a  very  basic 


MELTING   PROCEDURE  155 

nature,  borax  being  relied  upon  to  slag  the  impurities  and  thin  the 
charge,  but  too  great  an  excess  of  borax  will  make  the  slag  thick. 
If  the  slag  is  too  thick  and  yet  is  basic,  and  it  is  deemed  inadvisable 
to  add  more  borax,  then  silica  should  be  added,  which  may  be  in 
the  form  of  fine  quartz  tailing  free  from  slime,  since  the  slow- 
settling  slime  is  mainly  clay — silicate  of  alumina — rather  than  pure 
silica.  The  appearance  of  graphite  in  the  slag  indicates  that  the 
crucible  is  being  attacked,  and  usually  means  that  more  silica  should 
be  added. 

For  melting  an  ordinary  retort  sponge,  a  small  amount  of  flux 
consisting  of  two  or  three  parts  by  weight  of  borax-glass  and  one  of 
soda,  and  'poling'  with  an  iron  rod,  if  the  amalgam  contained  much 
sulphide,  is  all  that  will  be  required  in  the  way  of  fluxing.  After 
the  metal  and  slag  have  subsided  to  a  quiet  fusion,  the  mass  is 
stirred  with  an  iron  rod  that  has  been  previously  heated  red  hot 
that  no  gold  may  adhere,  the  object  being  to  settle  any  shots  of  metal 
in  the  slag  and  to  render  the  gold  homogeneous.  The  crucible  is  then 
lifted  from  the  fire  by  means  of  suitable  tongs  and  its  contents  are 
poured  into  an  iron  mould,  which  has  previously  been  well  coated 
on  the  inside  and  heated.  The  slag  rises  on  top  of  the  metal  and  may 
overflow  the  mould  without  doing  any  harm,  if  it  be  quite  fluid, 
while  the  gold  by  its  greater  weight  or  specific  gravity  sinks  down 
through  the  molten  slag  and  is  retained  in  the  mould.  It  is  im- 
probable that  any  shots  of  gold  that  will  not  settle  while  in  the 
furnace  will  do  so  after  pouring,  so  all  slag  from  gold  melts  should 
be  carefully  examined  for  shot  gold. 

The  mould  should  be  smooth  and  clean  on  the  inside,  all  rust,  old 
slag,  or  metal  should  be  removed.  It  should  be  given  a  coating  on 


BULLION    MOULD. 

(Braun-Knecht-Heimann  Co.,  San  Francisco.) 

the  inside,  preferably  of  carbon.  This  may  consist  of  a  mixture  of 
lampblack  and  lubricating  oil  having  the  consistence  of  soft  butter. 
Or  it  may  be  a  coat  of  soot  given  by  inverting  the  mould  over  burn- 
ing pitch  pine,  resin,  or  oiled  waste.  Whitewash  can  be  used.  Thick 
oil  has  been  used,  but  it  sputters  while  pouring  and  afterward  burns 


156  SAMPLING   BULLION 

with  a  disagreeable  smoke  and  odor.  The  purpose  of  this  coating 
is  to  prevent  the  gold  from  sticking  to  the  sides  of  the  mould  and 
to  allow  the  bar  to  come  out  easily.  The  mould  should  be  well 
warmed,  but  not  excessively,  before  being  used,  that  it  may  not  be 
cracked  by  the  introduction  of  the  hot  metal,  and  that  the  gold  and 
slag  may  not  be  suddenly  chilled,  interfering  with  forming  a  neat 
smooth  bar.  The  mould  is  finally  leveled  that  the  bar  may  be  of  an 
even  thickness.  Usually  the  mould  is  placed  at  a  right  angle  to  the 
flow  from  the  melting  pot,  but  a  neater,  easier  pour  can  be  made  by 
setting  the  length  of  the  mould  in  the  line  or  direction  of  the  pour. 
Greater  homogeneity  can  be  given  the  bar  for  the  purpose  of  sam- 
pling by  continually  moving  the  entering  stream  of  metal  up  and 
down  the  length  of  the  mould  in  pouring. 

After  the  gold  and  slag  have  cooled  sufficiently  to  become  solid, 
they  are  dumped  out  of  the  mould  into  a  tub  or  sink  of  water,  which 
usually  causes  the  slag  to  separate  easily  from  the  gold.  The  bar  is 
cleaned  by  knocking  and  scrubbing  off  any  bits  of  slag,  or  by  setting 
back  in  the  melting  pot  until  hot  and  then  plunging  it,  first  into 
dilute  sulphuric  acid,  and  then  into  water.  Nitric  acid  is  also  used. 
If  the  bar  looks  very  base  and  dirty,  it  may  be  re-melted  and  re- 
fluxed.  Two  opposite  corners  are  chipped  off  for  assay,  or  it  is  bored 
in  from  four  to  eight  places  with  a  %-in.  drill,  rejecting  the  sur- 
face borings ;  the  latter  method  of  sampling  is  to  be  preferred. 
Some  use  graphite  rods  for  stirring  the  molten  bullion ;  these  are 
either  purchased  or  are  made  by  cutting  a  section  out  of  an  old  or 
condemned  crucible  in  the  shape  of  the  lower  part  of  a  golf  club. 
A  small  hole  is  bored  in  the  toe  of  the  stirrer.  After  stirring  the 
bullion,  the  gold  caught  in  the  hole,  amounting  to  half  a  gram  or 
more,  is  poured  into  a  basin  of  water ;  this  is  repeated  three  or  four 
times  and  the  bullion  assay  made  from  the  granules  obtained  in  this 
way.  A  dip  sample  taken  in  this  way  is  more  accurate  than  any 
bar  sample. 

Recovering  Gold  from  Slag,  Old  Screens,  Etc. — The  slag  from  the 
meltings,  likewise  old  melting  crucibles,  are  saved  and  eventually 
run  through  the  clean-up  barrel  in  a  separate  charge  to  recover  any 
shots  of  gold.  The  slag  can  be  sent  through  the  battery  if  there  is 
no  clean-up  barrel  available,  but  the  crucibles  should  be  crushed 
otherwise  and  panned,  as  the  graphite  is  harmful  to  the  plate  amal- 
gamation. After  this  treatment  the  tailing  should  be  assayed,  as 
it  may  still  contain  sufficient  gold  to  warrant  shipping  to  a  smelter ; 
it  has  been  cyanided,  but  with  poor  extraction. 

The  wood  removed  from  the  mortars,  together  with  old  screen- 


AMALGAM    FROM    MILL   REFUSE  157 

frames,  and  all  wood  or  canvas  likely  to  contain  any  amalgam 
should  be  burned  and  the  ashes  put  through  the  clean-up  barrel,  or 
the  mortars  in  lieu  of  a  barrel  or  pan.  The  burning  is  sometimes 
accomplished  in  the  stove  installed  for  the  comfort  of  the  millmen, 
the  ashes  of  which  are  regularly  emptied  into  the  mortars.  This 
method  cannot  be  used  where  cyanidation  follows  because  of  the 
tendency  of  carbon  to  precipitate  gold  and  silver.  The  worn-out 
screens  should  be  thoroughly  scrubbed  and  pounded  after  being 
taken  from  the  frames,  to  remove  any  amalgam,  and  then  placed  in 
a  heap.  Shoes  and  dies  and  pieces  of  iron  from  the  mortars  should 
be  scrubbed  and  hammered  and  the  'eyes'  of  amalgam  in  the  blow- 
holes picked  out  by  means  of  old  round  files  tapered  down  to  a  point, 
finally  being  consigned  to  a  pile.  The  fine  iron  removed  from  the 
amalgam  should  be  placed  in  shallow  tubs.  The  oxidation  of  these 
screens  and  coarse  and  fine  iron  and  steel  should  be  promoted  by 
occasionally  adding  salt  and  frequently  wetting  with  water.  After 
being  reduced  to  rust  as  far  as  possible,  that  material  which  will 
enter  the  clean-up  barrel  should  be  ground  up  in  it  with  a  small 
amount  of  mercury  and  finally  dropped  into  water,  puddled,  and 
the  finer  iron  removed  by  a  magnet.  It  may  be  necessary  to  re-wash 
this  finer  material.  The  screens  and  coarse  iron  receive  a  thorough 
scrubbing  and  pounding  before  being  finally  thrown  out.  Roasting 
or  burning  the  screens  and  fine  iron  is  a  quick  way  to  loosen  the 
adhering  amalgam  and  to  promote  oxidation. 


PART  III 

GENERAL 


CHAPTER  IX 

Loss  OF  GOLD  IN  AMALGAMATION  AND  ITS  EEMEDIES — SIZING  AND  MILL 
TESTS — SAMPLING — MILLING  SYSTEMS. 

Loss  of  Gold  in  Amalgamation  and  Its  Remedies. — The  loss  of 
gold  in  amalgamation  may  be  due  to : 

1.  Free  gold  included  in  or  surrounded  by  the  gangue  rock. 

2.  Gold  that  is  chemically  combined  in  the  tellurides  or  mechan- 
ically enclosed  in  the  sulphides. 

3.  'Float'  gold  that  is  carried  along  on  top  of  or  suspended  in 
the  pulp,  and  which  does  not  come  in  contact  with  the  amalgamated 
plate. 

4.  'Rusty'  or  coated  gold. 

5.  'Overstamping.' 

6.  Poor  amalgamation  due  to  the  methods  in  use. 

7.  Poor  amalgamation  due  to  deleterious  substances  in  the  ore. 
First:  If  the  loss  is  in  the  free  gold  included  in  or  surrounded  by 

the  gangue  rock,  a  sizing  test  will  reveal  it  by  the  higher  value  of 
the  coarser  sands.  In  some  cases  the  coarser  sands  can  be  crushed 
finer  in  a  hand  mortar  and  panned  to  show  a  'prospect'  of  free  gold. 
The  correction  for  this  is  to  crush  finer,  not  the  ore  in  general,  but 
these  coarser  grains.  This  crushing  is  better  accomplished  by  using 
a  finer  screen  with  the  same  or  a  lower  height  of  discharge.  Run- 
ning two  batteries  with  different  size  screens  in  competition  with 
each  other  and  comparing  the  tailing  assays  will  determine  in  an 
empirical  way,  but  sizing  tests  in  connection  with  this  is  necessary 
for  a  true  diagnosis  of  the  conditions. 

Second :  Gold  in  association  with  tellurium  is  chemically  com- 
bined and  can  only  be  saved  by  cyanidation  along  special  lines,  by 
chlormation,  or  by  smelting,  and  rarely  by  concentration. 

Gold  in  the  sulphides  is  mainly  in  a  free  state,  finely  divided,  and 
mechanically  held  by  the  sulphides.  This  gold  is  usually  saved  by 
concentration,  and  in  some  cases  by  cyanidation  of  the  tailing  with- 
out concentration.  However,  a  part  of  it  can  be  amalgamated,  as  in 
the  Gilpin  County  practice,  by  the  use  of  -a  wide  mortar,  deep  dis- 
charge, long  and  slow  drop,  and  an  attempt  to  catch  the  gold  inside 
the  mortar.  Here  the  sulphide  because  of  its  higher  specific  gravity 
sinks  to  the  bottom  and  is  held  longer  in  the  mortar  than  the  bal- 

161 


162  FLOAT    GOLD 

ance  of  the  pulp,  allowing  the  gold  to  be  liberated  by  the  thorough 
sliming  of  the  sulphide,  and  to  be  brought  in  long  contact  with  the 
mercury  and  inside  plates.  This  process  has  had  slight  application 
outside  of  the  locality  mentioned,  where  it  was  necessitated  by  a 
large  proportion  of  the  gold  being  contained  in  the  sulphide  that 
was  of  too  low  a  grade  to  ship  and  smelt  profitably.  Part  of  the 
loss  in  the  tailing  may  be  due  to  sulphide  crushed  so  fine  (slimed) 
that  it  cannot  be  caught  on  the  concentrators ;  this  will  be  consid- 
ered under  'Overstamping.'  The  amalgamation  of  the  gold  in  the 
sulphide  has  been  accomplished  by  grinding  it  in  amalgamating 
pans,  tube-mills,  or  arrastres,  but  the  extraction  has  never  been  high, 
so  that  it  is  now  preferable  to  cyanide  it  if  it  contains  no  interfering 
elements,  or  to  ship  it  to  the  smelters.  However,  there  are  local 
conditions  or  peculiarities  of  the  metallurgical  practice  under  which 
it  may  be  highly  advisable  to  reduce  the  value  of  the  sulphide  to  be 
shipped,  smelted,  or  cyanided  by  preliminary  fine  grinding  and  amal- 
gamation. And  this  question  should  be  thoroughly  investigated, 
both  in  existing  plants  and  in  designing  new  plants. 

Third:  'Float'  gold  really  refers  to  that  gold  which  occurs  in 
flakes  so  light  and  thin  that  it  is  floated  along  on  the  surface  of  the 
pulp,  perhaps  buoyed  up  by  a  bubble  of  air ;  but  in  most  cases  it  will 
be  found  to  be  gold  so  fine  that  it  is  carried  suspended  in  the  pulp 
and  gets  no  opportunity  to  come  in  contact  with  the  amalgamated 
plate.  When  an  ore  containing  visible  gold  is  pounded  up  in  a  hand 
mortar  and  panned,  the  gold  is  found  to  be  pounded  into  scales  or 
into  infinitesimal  bits,  depending  on  the  nature  of  the  gold.  It  is 
doubtful  if  much  gold  is  overstamped  to  an  extent  producing  scales 
so  thin  that  they  will  float  on  the  surface  of  water  like  gold-leaf, 
although  such  gold  has  been  found  in  both  mills  and  placers;  but 
it  can  be  understood  that  gold  which  is  powdered  fine  may  be  car- 
ried along  in  the  pulp  clear  of  the  plates,  though  it  really  does  not 
float.  The  loss  attributed  in  a  tentative  way  to  float  gold  is  found 
by  assaying  the  flocculent  slime  of  the  tailing.  Should  this  show  a 
value  as  high  or  higher  than  the  sand,  it  would  indicate  overstamp- 
ing,  and  adjustments  calculated  to  prevent  this  should  be  made.  A 
part  of  the  value  lost  in  the  tailing  and  assigned  to  float  gold  is  in 
the  slimed  sulphide,  but  only  a  part  of  the  loss  can  be  rightly  as- 
cribed to  this. 

Perhaps  the  easiest  explanation  is  to  say  that  the  loss  consists  of 
gold,  sulphide,  and  amalgam  in  microscopic  particles,  which  is  both 
coated  with  slime  to  an  extent  that  prevents  it  from  amalgamating 
and  is  held  suspended  in  the  pulp  by  the  slime.  Increasing  the  grade 
of  the  plates  and  using  as  little  water  as  possible  in  the  mortar  to 


RUSTY  GOLD  163 

secure  a  better  wave  motion  and  contact  between  the  pulp  and  the 
plates,  together  with  making  the  plates  longer  and  keeping  them 
covered  with  a  bed  of  soft  amalgam,  will  aid  in  saving  more  of  the 
fine  and  float  gold.  If  the  battery  water  is  being  re-used  it  should 
be  well  settled,  for  as  the  water  or  pulp  becomes  thicker  and  more 
slimy  it  will  carry  off  more  of  this  light  gold.  Patent  amalgamators 
for  catching  this  kind  of  gold  should  be  tried.  It  is  practically  im- 
possible to  determine  the  form  or  condition  of  the  gold  in  the  slime 
where  the  amalgamation  and  concentration  has  been  capably  done, 
or  to  hope  to  promote  any  further  extraction  by  laboratory  and 
amalgamation  tests ;  reliance  must  be  placed  on  less  sliming  and  on 
cyanidation. 

Fourth :  '  Rusty '  gold  is  free  gold  covered  with  a  film  of  some  sub- 
stance other  than  air  or  the  gangue  rock  in  which  it  is  contained. 
This  may  be  due  to  an  oily  or  greasy  mineral  peculiar  to  the  ore,  like 
graphite ;  to  an  oxide  of  iron  or  copper,  or  to  other  compounds  of 
the  base  metals;  to  silicates  of  magnesia  or  alumina;  or  to  slime 
arising  from  crushing  the  ore.  This  film  prevents  the  gold  from 
coming  in  direct  contact  with  the  mercury.  Gold  to  amalgamate 
must  be  clean,  so  that  it  may  be  readily  wetted  by  the  quicksilver. 
When  gold  is  dirty,  rusty,  or  coated,  and  the  contaminating  material 
does  not  amalgamate  with  quicksilver,  then  the  quicksilver  through 
its  surface  tension  is  negative  and  strongly  repellant  of  the  con- 
taminating material  and  its  more  or  less  enclosed  golden  grain. 
Rusty  gold  can  sometimes  be  detected  by  panning  the  tailing  and 
examining  the  concentrate  with  a  microscope.  This  gold  should  be 
caught  by  the  concentrators,  or  in  the  cyanide  plant  if  not  too  coarse, 
also  by  the  use  of  riffles  or  blanket  tables.  To  amalgamate  this  gold 
it  must  be  made  clean  by  being  scoured.  This  can  be  done  by  using 
a  high  discharge,  preferably  with  a  coarser  screen  and  a  narrow 
mortar  that  the  tendency  to  overstamp  may  be  reduced.  With  a 
low-discharge,  rapid-crushing  mortar,  the  ore  is  in  the  mortar  an 
average  of  four  or  five  minutes,  this  length  of  time  can  be  doubled 
or  trebled  by  increasing  the  height  of  discharge,  so  that  the  par- 
ticles of  gold,  especially  the  heavier  ones,  are  subjected  to  the 
scouring  and  attrition  of  the  stamp  and  the  pulp  for  an  increased 
length  of  time.  Sodium  amalgam  in  the  mercury  should  be  tried. 
If  any  of  this  gold  is  retained  in  the  traps,  they  should  be  cleaned 
often,  perhaps  at  each  plate  dressing,  the  sand  being  ground  in  the 
clean-up  barrel  with  some  additional  mercury,  to  scour  and  amal- 
gamate this  gold.  Theoretically,  coarse  crushing  in  the  mortar  fol- 
lowed by  regrinding  and  amalgamating  in  a  pan  or  roller  mill 
should  be  successful.  It  is  considered  that  the  pan  amalgamator 


164  OVERSTAMPING 

will  amalgamate  gold  that  no  other  method  of  amalgamation  will 
save. 

Fifth:  ' Overstamping '  is  holding  the  pulp  longer  in  the  mortar 
subject  to  the  action  of  the  stamps  than  is  necessary,  thereby  pul- 
verizing it  finer  than  is  required  or  is  beneficial.  While  the  capacity 
is  reduced,  the  term  properly  has  no  reference  to  that,  but  to  the 
treatment  the  ore  receives  causing  it  to  give  a  reduced  extraction. 
Experiments  have  shown  that  a  hammered  gold  is  not  readily  amal- 
gamable,  and  further  experiments  tend  to  prove  this  to  be  due  to 
the  gold  being  covered  with  a  film  of  dirt  vand  grease  in  the  process 
of  hammering,  which,  in  connection  with  its  increased  density,  does 
not  allow  it  to  be  so  easily  wetted  by  the  mercury.  As  has  been 
observed  under  float  gold,  it  is  improbable  that  much  gold  which 
can  be  hammered  into  a  scale  is  rendered  non-amalgamable  by 
stamping  in  the  mortar,  especially  in  the  presence  of  mercury ;  while 
there  is  no  doubt  that  gold  in  the  allotropic  form  of  being  brittle 
can  be  stamped  so  fine  that  it  is  hard  to  catch  in  the  mortar  or  on 
the  plates,  particularly  if  it  is  covered  with  slime.  The  danger  of 
overstamping  is  augmented  with  increase  in  the  grade  and  per- 
centage of  the  sulphide.  The  Gilpin  County  practice  is  an  ideal 
illustration  of  overstamping  sulphide. 

As  to  whether  the  ore  is  being  overstamped  or  not  is  judged  from 
the  sizing-test  assays  taken  in  connection  with  the  tonnage  and 
operating  expenses.  If  the  assays  of  the  slime  and  fine  sands  closely 
approach  or  are  higher  than  those  of  the  coarser  sands,  adjustments 
should  be  made  that  will  reduce  the  percentage  of  fine  material  in 
favor  of  a  higher  tonnage.  If  it  is  an  actual  case  of  overstamping, 
resulting  in  the  gold  being  rendered  less  amalgamable  by  being 
hammered,  broken  up,  or  coated  with  a  film,  or  the  sulphide  being 
slimed,  the  proper  change  of  adjustments-  should  reduce  the  assays 
of  the  slime  and  finer  sands.  The  changes  of  adjustment  have  one 
object  in  view — to  get  the  pulp  out  of  the  mortar  as  quickly  as 
possible  after  having  been  crushed  to  the  proper  size  to  liberate  the 
gold  and  sulphide  from  their  matrix. 

Sixth:  Poor  amalgamation,  due  to  the  methods  in  use,  may  be 
caused  by  the  following:  To  keeping  the  amalgam  so  hard  that  it 
becomes  crystalline  and  breaks  away,  or  that  it  reduces  the  tendency 
of  the  gold  to  catch.  To  keeping  the  plates  so  wet  that  the  mercury 
and  amalgam  run  down  into  the  trap.  To  the  gold  not  catching  due 
to  stains,  bare  spots,  plates  cleaned  too  close,  too  much  water  used, 
or  too  small  a  plate  area.  To  loss  of  amalgam  by  not  removing  or 
bedding  down  the  crumbs  when  dressing  the  plates.  To  use  of  im- 
pure mercury.  To  grease  falling  into  the  mortar  and  contaminating 


FOULING   OF   MERCURY   IN   AMALGAMATION  165 

the  plates.     In  fact,  to  bad  practice  in  any  of  the  various  details 
connected  with  amalgamating. 

Seventh :  Poor  amalgamation  due  to  deleterious  substances  in  the 
ore  does  not  often  occur.  Arsenical  and  antimonial  ores  are  the 
worst  offenders  in  this  regard.  They  tend  to  foul  the  mercury  and 
amalgam,  coating  it  with  a  film  of  the  slimed  material  so  that  the 
mercury  does  not  readily  amalgamate  with  the  gold,  but  is  sickened 
and  a  large  part  of  it  lost.  This  trouble  is  liable  to  occur  to  some 
extent  with  any  base  and  heavily  sulphureted  ore.  The  principal 
remedy  where  the  loss  of  mercury  is  great,  is  to  practise  outside 
amalgamation;  though  in  cases  where  the  outside  plates  become 
coated  and  fouled,  it  may  be  necessary  to  attempt  to  catch  and  hold 
the  gold  within  the  mortar.  Crushing  in  cyanide  solution  may  assist 
the  amalgamation  in  so  far  as  the  cyanide  solution  will  tend  to 
keep  the  mercury  and  amalgam  in  better  condition.  Clayey,  tal- 
cose,  and  other  slimy  ores  sometimes  give  trouble  in  a  similar  way, 
or  by  coating  the  gold. 

Sizing  and  Mill  Tests. — In  making  mill  tests  two  batteries  should 
be  selected  that  receive  a  feed  as  nearly  identical  as  possible.  Com- 
parative tests  should  be  made  simultaneously  with  the  different  ad- 
justments. Sizing  of  the  tailing  samples  from  these  two  batteries 
should  exhibit  the  characteristics  of  the  ore  under  the  different  treat- 
ments. These  tests  may  be  conducted  in  the  following  manner. 
Each  tailing  sample,  understood  to  have  been  carefully  taken  and 
in  every  way  representative,  is  drained  of  its  settled  water,  dried, 
and  thoroughly  mixed.  A  quantity  of  from  30  to  60  oz.  is  removed 
for  the  sizing  test,  a  'head'  assay  sample  is  also  taken.  All  assays 
should  be  made  in  duplicate.  The  sizing  sample  is  panned  and  re- 
panned  until  all  the  concentrate  is  removed,  this  concentrate  to  be 
examined  for  rusty  gold  and  amalgam.  The  sample  together  with 
the  water  used  in  panning  is  now  thoroughly  stirred,  and  after 
settling  for  a  moment,  the  slimy  water  is  poured  off,  care  being 
exercised  that  no  sand  passes  over  with  it.  More  water  is  added  to 
the  sand  and  the  process  repeated  again  and  again  until  only  the 
granular  sand  remains  and  the  water  contains  slime  that  is  a  true 
fiocculent  slime,  one  that  is  light  and  feathery,  that  agglomerates, 
that  does  not  readily  settle  in  water,  and  that  makes  water  muddy, 
in  centra-distinction  to  sharp,  granular  sand  which  readily  settles 
and  does  not  make  water  muddy.  The  sand  is  sized,  either  before 
or  after  drying,  into  a  coarse,  medium,  and  fine  sand. 

The  testing  screens  should  be  shaken  or  tapped  to  the  same  ex- 
tent in  obtaining  each  size  and  in  each  test,  for  continued  shaking 


166  SIZING   TEST 

results  in  working  more  ore  through  the  screen  and  thus  making 
the  results  more  variable  and  of  less  value  for  comparison  ;  also,  a 
single  set  of  screens  should  be  used,  for  there  is  liable  to  be  a  marked 
variation  in  the  openings  of  two  screens  labeled  as  of  the  same  mesh. 
Where  comparative  tests  are  not  being  made  on  two  batteries,  a 
fourth  size,  an  extra  coarse  sand,  should  be  made.  Thus,  when 
crushing  through  a  30-mesh  screen,  by  making  an  extra  coarse  size 
out  of  that  held  on  a  40-mesh  screen,  we  may  be  able  to  judge  how 
the  ore  held  on  it  will  act  when  crushed  to  pass  through  a  40-mesh 
screen.  The  sand,  slime,  and  concentrate  are  now  dried,  weighed, 
and  assayed,  after  which  the  results  may  be  tabulated.  The  follow- 
ing is  taken  from  a  note  book,  and  is  an  actual  test  made  on  a  small 
lot  of  tailing  that  was  dried  before  being  weighed  for  the  sizing 
test: 

MILL  TEST,  G  -  MINE.     NOV.  7,  '05. 

(No.  35  brass  wire  screen.     5-in.  discharge.     Head  assay,  $1.30.     Weight 
taken,  600  grams.) 

Value  of  this 

Weight:  Assay         size  in  1  ton 

value.  of  tailing. 

$1.40  $0.19 

1.40  0.22 

1.40  0.18 

1.20  0.23 

1.00  0.39 


594  100.0  $1.21 

The  deductions  from  the  above  test  are  that  the  concentration  is 
perfect,  but  that  the  ore  is  being  crushed  too  fine  for  the  purpose 
of  economic  amalgamation,  since  the  assay  of  the  slime  is  compara- 
tively high  and  the  quantity  abnormally  large,  while  the  coarse 
sand,  that  held  on  '40-mesh,'  assays  no  more  than  the  finer  sand. 

The  results  of  a  single  sizing  test  should  not  be  taken  as  con- 
clusive, but  a  series  made.  The  capacity  may  be  obtained  by  catch- 
ing the  pulp  in  a  tub  or  barrel  for  a  certain  length  of  time  and 
weighing  the  dry  pulp.  Where  cyanidation  follows  amalgamation 
and  concentration,  the  adjustments  of  the  battery  will  be  de- 
termined by  the  sizing  tests  of  the  cyanided  tailing,  which  indicate 
how  fine  the  ore  should  be  crushed  to  get  the  maximum  extraction 
by  the  cyanide  solution. 

Generally  too  little  attention  ia  given  to  testing  and  studying  an 
ore  before  erecting  a  mill,  though  the  stamp-battery,  thanks  to  its 


Size. 
Held  on     40  mesh  

Grams.  Per  cei 
80  13.4 

Held  on     60   mesh  
Held  on   100   mesh  
Passed  100  mesh  
Flocculent   slime    

93  15.7 
77  13.0 
112  18.9 
232  39.0 

Concentrate    . 

,     none  found 

LABORATORY   AMALGAMATION   TEST  167 

wide  range  of  adaptability,  can  invariably  be  made  to  do  satisfactory 
work,  consequently  the  change,  if  any,  usually  takes  place  in  the 
concentrating  and  cyaniding  departments.  The  usual  procedure  is 
to  take  a  sample  of  the  ore  which  is  seldom  representative  of  the 
run-of-mine  ore.  This  ore  will  probably  come  from  a  dump,  or  near 
the  surface,  and  be  an  oxidized  ore,  while  the  assay  value  will  be 
high.  After  making  a  trial  run  at  a  testing  works,  a  mill  will  be 
ordered  by  the  directors  of  the  company,  the  details  of  the  mill  be- 
ing left  to  the  machinery  supply  house.  The  mill-site  may  be  selected 
and  the  mill  designed  by  a  man  who  has  had  little  or  no  experience 
in  milling.  Finally,  the  mill  is  completed  and  turned  over  to  the 
millman  who  must  then  spend  considerable  time  in  changing  and 
rearranging.  It  is  incomprehensible  why  mining  companies  so  sel- 
dom employ  competent  metallurgists,  independent  of  machinery 
supply  houses  and  special  process  companies,  to  examine  the  ores  of 
their  mines  and  to  design  and  build  a  mill  suited  to  those  particular 
ores  and  conditions.  The  cost  and  loss  of  time  in  changing,  rearrang- 
ing, and  providing  for  those  things  that  have  been  overlooked  would 
pay  for  the  metallurgist,  to  say  nothing  of  the  daily  saving  that  may 
be  effected  in  a  properly  designed  mill.  Such  a  man  should  more 
than  save  the  expense  of  his  fee  by  knowing  what,  how,  and  where 
to  buy. 

The  metallurgist  should  himself  take  representative  samples  of 
the  different  ores  and  make  laboratory  tests  in  amalgamation,  con- 
centration, and  cyanidation,  together  with  sizing  tests,  that  he  may 
thoroughly  understand  the  ore.*  For  making  amalgamation  tests 
two  methods  can  be  followed.  The  first  is  to  place  six  or  eigh 
assay  tons  of  the  ore  crushed  to  the  desired  mesh  in  a  large  glast 
bottle  with  sufficient  water  to  make  a  thin  pulp,  adding  yz  oz-  of 
mercury.  The  pulp  is  rolled  around  in  the  bottle,  is  lightly  shaken, 
and  is  given  a  panning  motion  for  some  time,  that  all  the  free  gold 
may  be  amalgamated.  The  contents  are  finally  washed  out  of  the 
bottle,  panned,  and  repauned  until  the  amalgam  is  separated  from 
the  pulp,  when  the  tailing  is  dried  and  assayed;  the  difference  be- 
tween the  head  and  tailing  assay  representing  the  amount  amalga- 
mated. If  mercury  that  contains  no  gold  has  been  used  in  this  test, 
the  gold  in  the  amalgam  can  be  determined  and  the  amount  amal- 
gamated ascertained  in  this  way.  The  amount  of  gold  is  found  by 
boiling  the  amalgam  in  dilute  nitric  acid  until  only  the  pure  gold 
remains,  when  it  can  be  washed,  dried,  annealed,  and  weighed  as 

"•Testing  ore  by  cyanidation  is  fully  described  in  the  chapter  on  'Ore  Test- 
ing and  Physical  Determinations  in  the  Author's  'Textbook  of  Cyanide 
Practice.' 


168  METALLURGICAL   DATA   REQUIRED 

usual  in  the  gold  assay;  or  the  amalgam  may  have  the  mercury 
driven  off  by  heating  it  in  the  open  where  there  is  no  danger  of 
salivation,  and  cupelling  the  resulting  sponge.  Mercury  entirely 
free  from  gold  can  seldom  be  obtained,  but  can  easily  be  prepared 
by  dissolving  it  in  dilute  nitric  acid,  when  the  gold  remains  undis- 
solved  and  can  be  filtered  off,  while  the  mercury  can  be  precipitated 
by  suspending  a  piece  of  copper  in  the  solution. 

A  better  method  of  making  an  amalgamation  test  is  to  work  the 
ore  as  a  thin  pulp  in  a  gold  pan  having  an  amalgamated  bottom,  as- 
saying before  and  after  treatment;  the  pan  being  used  at  the  same 
time  to  separate  any  sulphide  present.  Laboratory  amalgamation 
tests,  as  a  rule,  will  not  give  as  high  an  extraction  as  will  be  obtained 
in  actual  mill  practice.  This  may  be  due  to  the  fact  that  in  prepar- 
ing ore  for  such  a  test,  it  is  screened  frequently,  resulting  in  an 
evenly  sized  material,  whereas  in  actual  practice  a  large  proportion 
is  crushed  much  finer  and  should  give  a  higher  extraction.  It  is  also 
possible  that  the  dry  crushing  may  coat  the  gold  with  dirt  or  slime  so 
that  to  some  extent  it  resists  amalgamation. 

In  cyanide  practice  it  is  possible  in  nearly  every  case  to  determine 
by  laboratory  tests  the  extent  to  which  the  gold  can  be  dissolved, 
and  the  metallurgist  can  be  required  to  closely  approximate  this 
in  the  actual  work.  But  in  amalgamation  by  small  tests  it  is  im- 
possible to  determine  with  any  close  approximation  the  maximum 
amount  of  gold  that  can  be  amalgamated.  Therefore  the  ability  of 
the  millman  and  the  thoroughness  with  which  the  amalgamation  is 
being  accomplished  must  be  judged  from  the  results  attained  in 
actual  practice. 

The  points  it  will  be  necessary  for  the  metallurgist  to  know  are: 
What  percentage  of  the  gold  will  amalgamate  under  ordinary  crush- 
ing, and  what  increased  extraction  can  be  obtained  by  regrinding 
and  amalgamating  a  second  time.  What  percentage  of  concentrate 
there  is  in  the  ore,  its  nature,  value  per  ton,  and  amenability  to 
cyanide  .or  other  treatment.  What  extraction  can  be  secured  from 
the  ore  on  the  plates,  on  the  concentrators,  and  from  the  tailing  by 
cyaniding  with  coarse,  medium,  and  sliming  crushing.  Also  the 
nature,  occurrence,  and  condition  of  the  gold  in  the  ore.  Making 
tests  with  a  few  pounds  of  ore  has  been  decried,  but  while  such 
small  tests  are  not  conclusive,  they  are  a  reliable  guide  when  the  sam- 
ple represents  the  ore  fairly  and  the  tests  are  conducted  by  a  metal- 
lurgist experienced  in  the  processes.  They  will  enable  a  system  of 
treatment  to  be  outlined  that  should  be  tried  out  by  treating  a  few 
tons  of  the  different  classes  of  ore  at  a  testing  works  under  the  per- 


MILL-RUN   TEST  169 

sonal  direction  of  the  metallurgist,  and  with  the  same  devices  as 
those  to  be  installed. 

One  of  the  main  reasons  why  a  'mill  run'  should  be  made  with 
the  same  devices  as  those  to  be  installed  in  the  mill,  is  that  no  labora- 
tory crushing  can  exactly  duplicate  the  product  obtained  from  va- 
rious kinds  of  mills.  For  instance,  the  comparatively  clean,  angular, 
urislimed  particle  of  gold  or  sulphide  liberated  by  the  stamp,  and 
the  slimed,  ragged,  flaky  product  of  the  tube-mill  when  operated 
for  the  purpose  of  sliming — the  first  so  essential  in  amalgamation 
and  concentration,  the  other  so  desirable  in  the  cyanidation  of  cer- 
tain material.  Chemical  laboratory  tests,  such  as  by  cyanidation, 
may  be  relied  upon  to  quite  an  extent,  even  when  made  on  a  small 
scale.  But  where  the  process  is  mainly  a  mechanical  one,  mill  tests 
are  necessary  to  furnish  the  essential  mechanical  hints  and  to  indi- 
cate if  a  difference  in  the  crushing  will  make  any  difference  in  the 
final  results.  Yet  small  scale  mechanical  tests  will  furnish  many 
valuable  ideas  to  one  whose  familiarity  with  the  process  is  both  in 
the  mill  and  the  laboratory. 

The  extent  to  which  the  testing  should  be  carried  varies  with  the 
nature  of  the  ore  and  largely  with  the  degree  to  which  the  metal- 
lurgy of  similar  ores  in  that  locality  has  been  worked  out.  There 
are  some  districts  wrhere  it  seems  hardly  necessary  to  test  the  ore 
for  a  process,  such  as  the  Mother  Lode  of  California.  There  are 
other  districts,  however,  where  the  working  out  of  a  successful 
treatment  system  seems  to  almost  require  a  full-size  mill  operating 
under  the  actual  working  conditions,  such  as  was  seen  in  the  case 
of  the  silver  ores  of  the  Tonopah  district  of  Nevada. 

Sampling. — The  taking  of  mill  samples  should  be  done  as  auto- 
matically as  possible.  A  sample  of  the  battery  feed  taken  by  pick- 
ing it  by  hand  from  the  revolving  plate  of  the  feeder  is  unreliable  on 
account  of  taking  too  large  a  proportion  of  the  coarse  ore.  The 
sizing  of  a  battery-feed  sample  through  a  quarter  or  half -inch-mesh 
screen  will  usually  show  that  the  fine  material  assays  three  or  four 
times  as  much  as  the  coarse,  and  may,  in  some  rare  instances,  show 
the  reverse.  A  long  tin  trough  or  scoop  that  can  be  placed  beneath 
the  revolving  plate  and  catch  all  of  the  ore  as  it  drops  from  the 
feeder  will  give  a  very  good  sample  when  taken  hourly  or  half- 
hourly,  especially  if  the  fine  and  coarse  ore  are  well  mixed  in  the 
bin.  Where  outside  amalgamation  is  practised,  the  sample  of  the 
battery  feed  is  obtained  in  front  of  the  mortar  just  before  the  pulp 
strikes  the  plate. 

The  tailing  sample  should  be  taken  automatically  by  a  device 


170  SAMPLING   IN    MILLS 

for  that  purpose,  and  the  mill  man  should  be  under  instructions  not 
to  put  it  out  of  use  during  the  period  of  dressing  the  plates.  The 
millman  fears  that  loose  amalgam  will  be  washed  away  to  'salt'  the 
sample ;  but  if  amalgam  to  this  extent  is  being  lost,  immediate  steps 
to  prevent  it  should  be  taken.  Where  the  samples  are  taken  by 
hand  they  are  liable  to  become  'picked'  samples,  as,  for  instance, 
where  the  concentrator  man  carefully  adjusts  each  machine  before 
taking  the  tailing  sample.  For  catching  the  tailing  sample  from  an 
automatic  sampler,  the  usual  gasoline  can  may  be  used  with  a  light 
tin  pipe  3  or  4  inches  in  diameter,  fastened  to  a  few  pieces  of  wood 
which  allow  it  to  rest  on  the  can  with  its  bottom  end  projecting 
into  the  can.  The  pulp  flows  into  the  can  through  this  pipe,  and 
when  the  can  is  full  the  clear  water  commences  to  overflow  without 
any  attention  from  the  man  in  charge,  who  finds  the  pulp  well 
settled  when  he  comes  to  remove  the  sample. 

Milling  Systems. — Where  gold  will  amalgamate  to  the  extent  of 
20%  or  more,  amalgamation,  preferably  in  water,  may  be  practised. 
If  the  ore  will  not  amalgamate  to  this  extent  and  requires  cyanide 
treatment,  amalgamation  had  better  be  dispensed  with  unless  some 
of  the  amalgamable  gold  is  coarse  and  escapes  the  cyanide  plant 
through  the  inability  of  cyanide  solution  to  dissolve  coarse  gold. 
The  coarse  gold  in  an  ore  that  is  finely  ground  in  cyanide  solution 
by  a  tube-mill  can  be  expected  to  be  ground  so  fine  that  none  will 
escape  the  cyanide  plant  without  being  dissolved. 

Crushing  in  cyanide  solution  is  a  great  aid  to  cyaniding,  as  the 
ore  is  brought  promptly  into  contact  with  the  solution,  and  under 
conditions  that  cause  the  precious  metals  to  go  into  solution  quickly, 
thus  requiring  less  tankage  for  dissolving  the  gold.  It  also  permits 
using  a  certain  amount  of  water  in  washing  the  dissolved  gold  and 
silver  out  of  the  pulp  to  compensate  for  the  moisture  discharged 
in  the  tailing.  This  makes  a  saving  in  the  amount  of  cyanide  me- 
chanically lost,  and  in  practice  also  effects  a  saving  in  the  amount 
of  dissolved  gold  mechanically  lost.  Crushing  in  solution  has  its 
disadvantages  in  that  the  solution  throughout  the  mill  is  carrying 
quite  an  amount  of  gold ;  and  a  little  of  this  solution  is  constantly 
being  lost,  even  in  well  designed  mills,  by  the  leakages,  overflows, 
accidents,  and  otherwise.  There  is  an  abnormally  large  volume  of 
solution  to  be  cared  for,  pumped,  and  precipitated,  which  makes  a 
material  increase  in  the  costs  per  ton  of  ore  treated.  Another  dis- 
advantage of  crushing  in  cyanide  solution  in  a  mill  where  amalgam- 
ation is  being  practised,  is  that  a  part  of  the  gold  goes  into  solution 
which  would  be  amalgamated  if  the  crushing  was  done  in  water.  If 


CRUSHING   IN    WATER   VS.    SOLUTION  171 

this  gold  was  amalgamated,  practically  all  of  it  would  be  returned, 
but  by  going  into  solution  the  proportion  returned  is  lessened,  both 
through  the  losses  above  referred  to,  and  through  the  indifferent 
washings  of  the  filtering  devices  used.  The  amount  of  gold  going 
into  solution  that  could  otherwise  be  obtained  by  amalgamating  in 
water  will  vary  with  the  size  of  the  particles  of  gold ;  thus  with  an 
extremely  fine  gold  crushed  in  strong  cyanide  solution  as  much  as 
one-third  or  one-half  of  the  amalgamable  gold  may  be  dissolved  so 
quickly  that  it  cannot  be  amalgamated.  In  such  a  case  it  is  inad- 
visable to  crush  in  cyanide  solution.  Where  the  gold  is  coarse  and 
but  little  of  the  amalgamable  gold  enters  the  solution,  crushing  in 
solution  may  be  advisable,  depending  on  the  character  of  the  cyanide 
plant  and  the  perfection  of  its  operation  in  gathering  all  of  the 
dissolvable  precious  metal  into  the  clean-up. 

Where  the  sulphide  is  amenable  to  cyanide  treatment  and  is  small 
in  amount  or  low  in  value,  it  may  be  expedient  to  cyanide  it  with 
the  sand  without  concentration,  offsetting  the  decreased  extraction 
from  this  sulphide  by  the  lessened  cost  of  treatment.  At  one  promi- 
nent property  operating  along  this  line,  a  high  discharge  is  used  to 
retain  the  sulphide  longer  in  the  mortar,  that  it  may  give  a  higher 
extraction  in  the  cyanide  plant  through  being  crushed  fine,  while  a 
large  amount  of  water  is  used  in  the  mortar  to  increase  the  tonnage 
and  thus  compensate  for  the  decrease  due  to  the  high  discharge. 

Economic  problems  must  be  studied  when  considering  amalgama- 
tion and  cyanidation.  With  a  small  mill  of  10  or  20  stamps  obtain- 
ing a  good  extraction  by  amalgamation  and  concentration,  it  may 
not  be  advisable  to  put  in  a  cyanide  plant  taking  the  pulp  directly, 
on  account  of  the  high  cost  per  ton  of  capacity  for  installing  and 
operating  a  small  plant  of  this  type.  It  may  be  better  to  run  the 
tailing  into  a  pond  and  later  put  in,  at  less  tonnage  expense,  a  leach- 
ing plant  of  large  capacity.  With  a  pulp  crushed  through  a  30  or 
40-mesh  screen  and  properly  impounded,  it  is  possible  to  extract 
practically  all  of  the  dissolvable  gold  and  silver.  In  a  country  of 
average  working  costs,  an  impounded  tailing  having  a  value  of  80c. 
per  ton  and  giving  an  extraction  of  80%  will  return  a  good  margin 
of  profit.  As  the  plate  or  concentrator  tailing  becomes  higher,  the 
necessity  for  a  plant  to  treat  it  directly  increases,  since  the  tailing, 
pond  will  hold  a  large  amount  of  money  that  is  not  available,  and 
there  is  a  loss  from  the  sand  blown  away  and  an  occasional  break- 
ing of  the  dam.  A  tailing  pond  is  sometimes  a  desirable  thing  to  a 
manager,  or  promoter,  as  when  it  figures  prominently — too  promi- 
nently usually — in  the  report  of  the  assets  and  possibilities  of  the 
company's  property.  Regrinding  of  the  pulp  followed  by  amal- 


172  AMALGAMATION  AFTER  PINE-GRINDING 

gamation  (secondary  amalgamation)  may  reduce  the  value  of  the 
tailing  to  a  point  so  low  that  it  may  not  be  profitable  to  cyanide  it, 
and  this  point  should  be  looked  into  when  making  the  tests  pre- 
liminary to  designing  the  mill.  For  this  purpose  some  form  of 
grinding  pan,  a  Chilean  mill,  or  the  slow-speed  roller  mill,  that  will 
admit  of  amalgamation  within  the  mill,  may  be  recommended.  The 
tube-mill  has  been  found  the  most  satisfactory  machine  for  fine- 
grinding  for  cyanidation.  It  was  formerly  considered  a  poor  ma- 
chine for  amalgamating  purposes,  since  any  mercury  fed  to  it,  as 
well  as  the  gold  which  is  liberated,  is  supposed  to  come  out  thor- 
oughly slimed.  But  this  idea  is  passing  away,  for  excellent  outside 
amalgamation  can  be  effected  after  the  tube-mill,  as  due  to  the 
fineness  of  the  pulp,  a  beautifully  thin  flow  can  be  had  over  the 
plates.  When  crushing  in  cyanide  solution  the  grinding  and  sliming 
action  within  .the  mill  causes  so  much  of  the  gold  to  go  into  solution 
that  it  is  usually  not  worth  while  to  try  amalgamation  afterward. 

From  a  theoretical  standpoint  it  would  appear  that  where  amal- 
gamation or  concentration  is  to  follow  the  tube-mill,  the  mill  should 
be  run  at  a  speed  that  will  cause  the  balls  to  be  carried  part  way 
around  and  to  crush  by  their  falling  impact,  rather  than  the  slower 
rate  of  speed  whereby  comminution  is  effected  by  the  attrition  or 
rolling  and  grinding  of  the  pebbles  alone.  The  first  is  a  case  of 
cracking  open  the  grains  and  liberating  the  gold  or  sulphide  as  a 
relatively  large  angular  particle  susceptible  of  easy  amalgamation 
or  concentration,  whereas  the  second  results  in  the  scaly,  impalpable, 
unmanageable  slime  produced  by  attrition.  The  first  is  illustrative 
of  the  principle  of  the  stamp,  the  second  that  of  the  grinding  mill. 
An  appreciation  of  these  principles  will  lead  to  a  better  understand- 
ing of  the  reason  for  the  supremacy  of  the  stamp-mill. 

"Within  recent  years  fine-grinding  and  'all-sliming,'  invariably 
connected  with  crushing  in  solution,  have  rapidly  come  into  vogue. 
In  most  cases  it  has  been  advisable,  but  in  many  instances  these 
methods  have  been  employed  because  it  has  been  the  fad,  or  because 
filtering  devices  were  installed  that  required  them.  This  is  clearly 
wrong.  Fine-grinding  should  not  be  carried  beyond  the  economic 
point.  The  cost  of  finer  comminution  increases  rapidly,  whether  by 
stamp,  Chilean  mill,  tube-mill,  or  other  device.  The  degree  of  fine- 
ness that  will  give  the  highest  extraction  in  the  laboratory  is  not 
necessarily  the  one  that  will  give  the  most  profit.  The  milling  and 
cyaniding  machinery  should  be  susceptible  of  adaptation  to  the 
economic  requirements,  and  the  millman  or  metallurgist  should  pos- 
sess the  ability  to  find  them. 

It  may  be  given  as  a  rule  of  broad  application  that  the  higher 


ALL-SLIMING  173 

the  grade  of  the  ore  and  the  baser  it  is  toward  amalgamation,  the 
better  adapted  it  is  for  all-sliming  and  crushing  in  solution;  while 
the  lower  the  grade  and  the  less  base  it  is  toward  amalgamation,  the 
less  adapted  it  will  be  to  those  methods.  For  as  the  grade  of  ore 
increases  the  percentage  of  extraction  will  also  increase  somewhat, 
but  the  value  of  the  tailing  in  dollars  and  cents  will  likewise  in- 
crease. Finer  grinding  will  reduce  the  amount  in  the  tailing,  at 
least  when  cyanidation  is  used;  but  as  the  ore  becomes  lower  in 
grade  the  additional  amount  won  from  the  ore  by  finer  grinding 
rapidly  grows  less  until  it  is  overbalanced  by  the  increased  cost  of 
finer  grinding.  It  is  an  open  question  as  to  whether  crushing  in 
solution  decreases  the  working  costs  per  ton,  but  we  will  suppose  a 
case  in  which  it  does  and  in  which  cyanidation  is  necessary.  At  first 
sight  it  would  appear  best  to  dispense  with  amalgamation  and  catch 
the  gold  by  one  process  only — that  of  cyanidation — but  the  cost  of 
amalgamating  and  the  almost  negligible  loss  of  gold  in  amalgam- 
ating varies  but  slightly  with  the  amount  of  gold  amalgamated  per 
ton;  whereas  the  working  costs  per  ton  by  cyanidation  increase  as 
more  gold  is  dissolved  per  ton,  because  of  the  more  elaborate  equip- 
ment required  in  the  attempt  to  obtain  all  the  dissolved  gold,  also 
because  the  mechanical  loss  of  gold  grows  greater  as  the  amount  dis- 
solved per  ton  of  ore  increases.  Thus  it  follows  that  as  the  amount 
that  can  be  amalgamated  increases,  the  advisability  of  crushing  in 
solution  decreases.  The  correctness  of  this  principle  is. indicated 
by  the  reversion  from  attempting  to  remove  the  dissolved  gold  from 
the  ore  solely  by  filter  washing,  to  the  method  of  separating  as  much 
gold  as  possible  from  the  ore  by  preliminary  decantations  before 
sending  the  pulp  to  the  filter  for  final  washing.  What  better  method 
than  amalgamation  is  there  for  reducing  the  value  of  the  pulp  going 
to  the  filter,  and  lessening  the  mechanical  loss  and  perhaps  the 
working  costs  throughout  the  whole  process  of  cyanidation? 

It  is  a  fact  that  crushing  in  solution  has  been  generally  unsatis- 
factory on  low-grade  ore,  and  there  do  not  appear  to  be  any  plants 
operating  under  such  conditions  today — or  at  least  any  that  are 
widely  known  outside  of  the  Black  Hills,  yet  there  are  many  plants 
employing  final  cyanidation  on  low-grade  ore.  The  question  now 
comes,  if  crushing  in  solution  has  to  give  way  to  other  methods  on 
low-grade  ore,  why  are  not  these  other  methods  more  economical  on 
higher  grade  ore?  Various  factors  enter  into  the  consideration  of 
this  matter,  but  the  principal  reason  why  no  satisfactory  answer  has 
yet  been  made  appears  to  be  that  the  metallurgists  who  should  give 
us  the  answer  are  too  busy  boosting  special  processes  in  which  they 
are  interested. 


174  MILL   DESIGNING 

There  have  been  a  number  of  mills  built  to  employ  these  methods 
which  have  not  proved  successful.  These  have  usually  been  small 
mills,  either  not  elaborately  and  carefully  designed  or  embodying 
some  rather  new  and  untried  devices.  The  best  way  to  handle  these 
'novelty  mills'  is  to  go  back  to  proved  methods.  Crush  in  water 
and  amalgamate,  following  with  regrinding  and  secondary  amal- 
gamation. Get  all  that  can  possibly  be  obtained  by  amalgamation, 
for  that  will  be  'absolute,'  at  least  in  so  far  that  loss  of  amalgam- 
able  gold  cannot  be  detected  after  the  careful  amalgamator,  except 
by  the  '  eyes '  of  amalgam  appearing  in  the  tailing  flume.  Then  take 
the  tailing  to  the  cyanide  plant  and  do  the  best  that  can  be  done 
with  the  machinery  available. 

The  idea  should  be  borne  in  mind  in  designing  and  erecting  and 
in  starting  a  new  mill;  the  arrangements  should  be  such  that  the 
crushing  may  be  done  either  in  water  or  solution,  and  it  is  generally 
wise  to  start  crushing  in  water  and  effect  the  change  to  crushing 
in  solution  after  the  metallurgical  system  and  the  mill  equipment 
have  been  tried  out. 

In  general,  mills  should  be  designed  and  built  along  tried  and 
proved  lines,  for  then  it  can  be  foretold  with  confidence  just  what 
the  mill  will  accomplish,  especially  in  a  mechanical  way.  Thus  the 
successful  experience  of  others  can  be  utilized,  and  should  some  un- 
locked for  difficulty  arise,  precedents  will  be  at  hand  for  solving  it. 
Such  a  mill  can  be  started  without  a  long  and  costly  siege  of  loss  of 
time,  worry,  experiments,  and  alterations,  and  new  employees  will 
require  little  coaching.  Science  is  the  accumulated  knowledge  of 
the  ages  from  which  the  errors  have  been  removed,  the  rough  places 
straightened  out,  the  shoals  marked,  and  the  principles  made  clear. 
He  who  follows  in  its  footsteps  can  expect  a  fair  measure  of  success, 
but  he  who  throws  his  fortunes  with  what  science  and  practice  have 
not  yet  indicated  as  safe,  has  left  the  lighted  way  and  may  expect 
a  hard  path  and  usually  disaster.  Scientific  mill  designing  consists 
in  following  the  lighted  way,  and  if  this  does  not  promise  a  suffi- 
cient measure  of  success,  then  surely  the  untried  way  is  one  of 
danger.  To  be  more  concrete,  scientific  mill  designing  and  opera- 
tion consists  in  three  things:  First,  thoroughly  testing  the  ore  until 
all  necessary  information  is  obtained.  Second,  designing  and  build- 
ing a  mill  which  embodies  those  ideas  and  those  particular  devices 
which  practice  linked  with  science  have  indicated  to  be  the  most  reli- 
able and  advantageous  for  each  particular  part  and  purpose.  Third, 
after  the  mill  has  been  placed  in  successful  operation  along  conserva- 
tive lines,  experimenting  and  testing  with  various  machines,  devices, 
and  expedients — the  original  design  of  the  mill  to  include  the  idea  of 


CHILEAN    MILL  175 

facilitating  this — to  increase  tonnage  and  extraction  and  to  decrease 
costs.  The  first  two  will  insure  a  successful  mill.  The  last  will 
greatly  prolong  the  life  of  the  mine,  for  a  consideration  of  the  mines 
famous  for  long  and  continuous  production  will  show  that  they  are 
operating  on  low-grade  ore  with  a  remarkably  small  margin  of  profit 
per  ton,  and  a  margin  due  to  a  scientific  reduction  of  costs  and  in- 
crease of  extraction  begun  while  the  mine  was  in  good  ore. 

One  of  the  later  ideas  in  stamp-milling  has  been  to  employ  Chilean 
mills  as  intermediate  grinders  following  stamps.  This  is  with  the 
viewpoint  that  the  tube-mill  finds  its  greatest  efficiency  in  reducing 
30  or  40-mesh  material  to  200-mesh,  the  Chilean  mill  in  medium 
grinding,  and  the  stamp  in  coarse  crushing.  With  this  idea  it  has 
been  proposed  to  use  heavy  stamps  crushing  through  a  4  to  12-mesh 
screen,  delivering  to  Chilean  mills  grinding  through  a  30  or  40-mesh 
screen  to  tube-mills  sliming  to  the  desired  fineness.  However,  there 
has  come  contemporaneously  with  this  idea  a  rapid  increase  in  the 
weight  of  stamps  and  a  development  of  tube-milling  to  cover  a  wider 
range.  As  a  result  it  is  recognized  that  stamps  harnessed  to  tube- 
mills  make  a  combination  crushing  by  impact  that  is  so  efficient  that 
the  introduction  of  intermediate  grinding  mills  is  inadvisable.  The 
Chilean  mill  has  been  used  in  this  way  to  increase  or  double  the  ca- 
pacity of  existing  mills  without  erecting  more  ore-bins  and  stamps, 
by  being  placed  after  the  stamps  or  between  them  and  the  tube- 
mills.  The  same  result  can  be  effected  by  adding  more  tube-mills. 


CHAPTER  X 

MlLLMEN  AND  MlLL  CREWS — MlLL  MANAGEMENT — HANDLING  PlILF 
AND  TAILING; 

Millmen  and  Mill  Crews. — The  men  who  are  in  charge  of  stamp- 
mills  are  almost  invariably  good  mill  mechanics,  a  large  part  have 
graduated  out  of  machine  shops,  and  even  the  least  of  them  are 
first-class  'monkey-wrench'  machinists,  but  only  a  small  part  are 
metallurgists.  The  methods  of  many  of  them  are  those  that  they 
were  taught,  and  these  methods  they  apply  to  all  conditions  with 
but  little  variation.  This  lack  of  ability  to  initiate  experiments,  to 
test,  to  devise  new  methods,  and  to  progress,  has  hampered  the  ad- 
vancement of  the  stamp-mill  process.  It  is  seen  in  the  tenacity  with 
which  they  cling  to  the  old-time  idea  of  saving  the  maximum  amount 
of  gold  in  the  mortar,  when  the  same  and  in  some  cases  a  higher 
saving  could  be  obtained  by  giving  the  stamp-battery  a  chance  to 
perform  its  proper  function — to  prepare  the  ore  for  amalgamation, 
rather  than  to  amalgamate  it.  Wherever  the  millmen  have  forsaken 
the  well-beaten  path  of  trying  to  save  all  the  gold  possible  in  the 
mortar,  the  tonnage  has  increased  and  ease  of  operation  has  been 
promoted.  "Catch  the  gold  as  soon  as  you  can — catch  it  inside  the 
mortar, "  is  a  good  old  maxim,  but  the  slogan  of  the  millman  should 
be,  "Down  with  the  tailing  and  up  with  the  tonnage,"  and  not, 
"Increase  the  inside  catchment — keep  it  up  to  60  or  80  or  95%." 
The  millman  should  understand  adjusting  the  mill  to  the  peculiar 
requirements  of  the  ore,  that  he  may  be  able  intelligently  to  put  his 
slogan  into  actual  practice.  Pie  should  also  be  able  to  determine  the 
point  where  a  higher  tonnage  ceases  to  be  desirable  by  reason  of  re- 
sulting in  too  high  a  tailing,  the  economic  limit  having  been  reached. 

The  millman  should  have,  in  addition  to  training  in  large  and 
small  mills  in  various  localities,  and  in  mechanical  work  dealing  in  a 
general  way  with  the  setting  up,  operating,  and  repairing  of  ma- 
chinery, with  carpentering,  pipe  fitting,  and  construction  work,  a 
short  training  in  assaying  and  ore-testing,  and  some  study — home 
study  if  nothing  more — in  chemistry  and  mechanical  and  construct- 
ive drawing.  In  view  of  the  wide  application  of  electricity  as  the 
motive  power  for  mills,  the  millman  should  understand  the  use  and 
care  of  alternating-current  machinery.  While  it  is  not  expected 

176 


AMALGAM    STEALING  177 

that  he  should  be  able  to  set  up  transformers  or  connect  the  wind- 
ings of  motors,  he  should  understand  more  than  merely  to  start  the 
motor  according  to  the  printed  directions. 

Much  has  been  written  and  said  about  the  honesty  of  mill  em- 
ployees. One  of  the  principal  arguments  advanced  for  dispensing 
with  amalgamation  and  centralizing  the  recovery  of  gold  in  the 
cyanide  plant,  is  that  it  will  prevent  loss  of  amalgam  by  theft.  It 
has  been  the  fortune  of  the  writer  to  have  worked  and  associated 
with  many  millmen  in  various  parts  of  the  country,  and  to  have 
come  in  contact  with  them  on  an  equal  footing  and  under  condi- 
tions whereby  their  character  could  be  best  studied,  and  he  has  not 
known  of  a  case  of  amalgam  theft  or  a  suspicion  of  such,  except  by 
report. 

There  are  two  reasons  why  so  little  thieving  occurs,  despite  the 
fact  that  amalgam  stealing  appears  easy  and  safe.  The  first  is  the 
esprit  de  corps,  or  loyalty  to  the  profession,  which  is  as  strong  in  the 
millman  as  in  any  other  calling.  The  second  is  that  the  amalgam 
or  bullion  is  viewed  by  the  millman  as  so  much  merchandise  which 
he  is  accumulating  for  his  employer,  just  as  he  is  saving  the  sulphide 
in  the  concentrating  department.  It  is  an  actual  fact  that  millmen 
who  may  'high  grade'  when  working  in  the  mine,  or  on  the  rock- 
breaker,  will  take  no  amalgam  from  the  mill  and  nothing  more  than 
a  specimen  from  the  feeders. 

The  danger  of  amalgam  theft  lies  in  putting  a  green  man  of  .un- 
known character  in  a  mill  as  helper,  or  temporarily  on  clean-up  day. 
Also  in  the  employment  of  a  so-called  millman  who  is  only  following 
milling  until  he  can  find  an  easier  way  for  getting  the  living  that 
'the  world  owes  him.'  Outside  of  the  above  two,  the  danger  does 
not  lie  mainly  with  the  professional  mill  employee,  but  with  the  dis- 
honest manager,  superintendent,  or  confidential  man  who  does  the 
melting,  and  who  may  have  a  private  ingot  mold  of  his  own  to  fill. 

In  late  years  a  new  class  of  stamp-mill  superintendents  has  arisen ; 
these  are  the  cyanide  metallurgists,  who,  as  milling  and  cyaniding 
operations  are  becoming  more  closely  linked  together,  are  taking 
both  operations  in  charge.  Where  the  work  is  carried  out  in  con- 
junction, this  is  a  step  in  the  right  direction,  but  one  in  advance  of 
the  supply,  for  it  is  difficult  to  find  men  who  have  a  thorough  ex- 
perience in  stamp-milling,  amalgamation,  and  cyanidation,  mechan- 
ically as  well  as  metallurgically.  In  the  extended  acquaintanceship 
of  the  writer  there  is  only  one  past  master  of  stamp-milling,  amal- 
gamation, and  cyanidation,  who  is  able  to  direct  and  instruct  his 
subordinates  in  every  detail. 

The  tendency  of  these  new  mill  superintendents  who  have  little  or 


178  MILLMEN 

no  training  in  stamp-milling  and  amalgamation,  is  to  put  too  much 
stress  on  the  cyanide  branch.  These  are  the  men  who  would  grind 
all  the  ore  so  that  the  precious  metal  would  be  extracted  by  cyanide 
solution,  disregarding  the  fact  that  if  a  grain  of  gold  is  caught  on 
the  plates,  practically  100%  of  it  is  recovered;  whereas,  if  it  goes 
to  the  cyanide  plant,  a  little  of  it  is  lost  through  the  various  wastes 
of  solution,  the  cleaning  up,  and  through  the  imperfect  washings  of 
the  filters  used. 

The  stamp-battery,  to  do  good  work,  requires  to  be  in  the  hands 
of  a  man  who  is  in  immediate  charge  of  it,  one  who  is  a  good  mill- 
man  and  a  strict  disciplinarian,  a  crank  on  having  everything  done 
right  and  kept  in  condition,  stopping  just  short  of  the  point  where 
the  details  to  be  carried  out  become  idealistic  rather  than  practical 
and  beneficial.  The  average  competent  mill  employee  prefers  to 
work  under  these  conditions,  rather  than  where  no  system  prevails 
and  everything  is  racked  to  pieces  so  that  he  must  constantly  keep 
a  sharp  outlook  for  trouble  and  be  continually  repairing.  The  plac- 
ing of  a  stamp-battery  in  charge  of  a  master  mechanic  who  is  not 
an  experienced  millman  and  whose  attention  is  elsewhere  most  of 
the  time,  is  just  as  serious  a  mistake  as  to  consign  it  to  the  mercy  of 
the  different  shifts  of  employees,  all  of  whom  are  equally  responsible 
and  acting  without  a  directing  head.  A  man  may  be  a  first-class 
millwright  and  machinist  and  still  be  unsuited  by  lack  of  experience 
to  take  charge  of  a  mill.  A  mistake  is  made  in  placing  a  man  in 
charge  of  a  stamp-battery  whose  experience  has  been  superficial,  no 
matter  how  competent  he  may  appear;  the  result  of  such  error  is 
that  the  mill  gradually  wrecks  itself  until  it  becomes  so  badly  racked 
and  worn  and  generally  broken  down  that  it  is  a  nightmare  for  a 
millman  of  Jong  experience  to  work  in  it.  The  stamp-battery  is  such 
a  simple  machine  that  an  observing  man  can  learn  to  operate  it  under 
instruction  in  a  short  time,  but  being  ponderous  machinery  subjected 
constantly  to  jar,  tremendous  vibration,  and  high  tension,  to  insure 
long  life  and  good  health  it  must  have  a  man  in  charge  who  can 
promptly  recognize  its  symptoms  of  trouble  and  at  once  apply  the 
proper  remedies.  From  experience  and  observation  it  can  be  stated 
positively  that  it  is  a  wise  procedure  to  employ  only  the  highest 
class  of  millmen,  even  if  highly  priced,  for  such  men  increase  ton- 
nage and  extraction,  lessen  the  cost  for  repairs,  and  prolong  the 
life  of  the  mill  far  more  than  is  generally  known. 

A  few  words  may  be  added  for  the  novice  just  entering  stamp- 
mill  work.  Owing  to  the  noise  that  forbids  all  conversation  except 
that  absolutely  necessary,  the  apprentice  must  learn  largely  from 
observation  rather  than  by  direct  instruction.  Careful,  minute,  and 


LEARNING   STAMP-MILLING  179 

concentrated  observation  is  the  first  step,  for  stamp-milling  has  be- 
come a  highly  developed  craft  in  which  some  construction  can  be 
placed  or  some  fact  read  in  .details  so  small  that  they  can  hardly  be 
observed  by  the  inexperienced  man.  By  close  observation  and 
thoughtful  consideration  the  apprentice  is  able  to  observe  these 
details  and  interpret  their  meaning,  so  that  in  a  short  time  his 
attention  becomes  subconscious  and  therefore  no  longer  forced.  He 
learns  to  wear  engineer's  coats  or  'jumpers'  worn  as  a  shirt,  or 
other  tight-fitting  clothes  that  offer  no  loose  ends  to  be  caught  by 
belts  and  machinery;  to  use  methods  that  are  not  unnecessarily 
dangerous  to  life  and  limb  in  putting  belts  off  and  on,  hanging  up 
stamps,  setting  tappets,  and  working  on  the  stamps ;  to  never  drop 
a  stamp  until  he  is  sure  that  no  one  at  the  mortar  below  will  be 
caught  or  injured  by  it,  etc.  The  millman  operates  his  mill  largely 
by  sight  and  sound.  As  he  walks  by  the  stamps,  even  though  at 
some  distance  and  with  his  attention  preoccupied,  he  notes  any 
stamp  that  is  dropping  too  hard  or  that  is  too  much  cushioned; 
a  stem  that  has  pulled  out  of  its  boss,  or  has  lost  its  shoe,  or  is 
dropping  on  a  piece  of  steel  that  has  inadvertently  fallen  into  the 
mortar;  a  motar  that  is  running  empty;  the  coarse  oversize  due 
to  a  break  in  a  screen ;  or  any  of  the  details  that  may  need  rem- 
edying. Amid  the  awful  roar  he  is  able  to  differentiate  the  sound 
of  improperly  working  parts  from  those  working  properly.  If, 
while  he  is  in  a  distant  part  of  the  mill  shoveling  ore  in  an  almost 
empty  bin,  working  in  the  clean-up  room,  or  talking  to  a  friend 
outside  the  mill  door,  a  stamp  breaks,  pulls  out,  or  commences  to 
fall  on  a  piece  of  vagrant  steel,  a  tappet  begins  to  cam,  or  a  mortar 
to  run  empty,  his  trained  subconscious  mind  recognizes  the  peculiar 
jangle,  or  steady  clap-clap,  or  muffled  hollow  roar,  and  before  he 
realizes  it  he  is  started  and  perhaps  half  way  across  the  mill  on 
his  way  to  the  seat  of  trouble,  though  as  a  mill  becomes  racked  and 
worn  from  poor  condition  and  ill  use  it  becomes  more  difficult  to 
run  by  sound.  As  the  steam  engineer  judges  the  condition  his 
engine  is  in  by  its  movement  and  sound,  so  does  the  millman  judge 
his  mill;  but  unfortunately,  the  fact  that  the  stamp-mill  will  stand 
ill  use  and  abuse  as  well  as  answer  to  the  refined  control  of  a 
master  hand  has  led  many  to  consider  the  stamp-battery  as  a  relic 
of  medievalism,  fit  only  to  be  presided  over  by  a  low-browed, 
strong-armed  giant  equipped  with  a  sledge-hammer  and  an  inex- 
haustible stock  of  profanity  and  endurance. 

The  crew  of  a  10-stamp  mill  having  concentrators  will  be  com- 
posed of  one  man  per  shift.  The  man  on  the  day  shift  will  be  in 
charge  and  assisted  by  the  man  who  tends  the  rock-breaker.  A 


180  STAMP-MILL    CREWS 

20-stamp  mill  with  concentrators  has  been  run  by  the  same  size 
crew,  but  the  work  is  so  strenuous  that  men  will  not  long  remain 
and  the  company  suffers  a  direct  loss  during  their  stay  from  poor 
work,  especially  in  the  concentration.  One  batteryman  per  shift 
with  a  head  millman  can  run  40  stamps  and  do  the  amalgamating ; 
and  for  this  reason  it  is  an  economical  size  of  mill  to  build.  One 
man  per  shift  has  run  up  to  60  stamps  and  done  the  amalgamating, 
but  the  work  is  entirely  too  arduous  for  one.  The  crew  of  a  100- 
stamp  mill  will  consist  of  an  amalgamator  in  charge  of  the  shift,  one 
batteryman  who  attends  to  the  feeding,  and  one  helper.  On  the 
day  shift  there  may  be  a  repair  man  in  addition  to  the  head  millman. 
Should  the  ore  be  low  grade,  requiring  only  one  or  two  dressings 
of  the  plates  in  24  hours,  and  the  mill  be  in  first-class  condition,  the 
helper  on  each  shift  may  be  dispensed  with.  Should  amalgamation 
not  be  practised,  the  amalgamator  may  be  dispensed  with,  leaving 
one  man — the  batteryman — in  charge  of  the  100  stamps ;  but  a  first- 
class  mill  kept  in  splendid  condition  is  required  if  one  batteryman 
per  shift  with  a  head  millman  and  a  repair  man  on  the  day  shift 
are  to  operate  and  keep  in. repair  100  stamps.  The  mill  wood  work, 
such  as  making  screen-frames,  chuck-blocks,  and  other  small  matters 
of  this  kind,  is  done  in  the  mine  carpenter  shop. 

It  is  always  advisable  to  place  the  mine  air  compressor  in  the  mill 
of  a  small  or  moderate  size  property — unless  there  are  urgent 
reasons  for  placing  it  elsewhere — preferably  on  the  plate  floor  if 
there  is  no  steam  engineer  to  take  charge  of  it,  since  for  some  in- 
herent reason  not  readily  explainable  or  through  custom  the  battery- 
man rather  than  the  concentrator  man  seems  to  be  the  proper  indi- 
vidual to  care  for  it.  The  mistake  of  isolating  the  air  compressor, 
which  requires  a  constant  but  small  amount  of  attention,  at  a  point 
where  a  compressor  man  is  required  to  watch  it  when  it  could  just 
as  well  be  cared  for  by  one  of  the  mill  employees,  is  often  observed. 
Cases  have  been  noted  where  the  compressor  has  been  located  under 
the  same  roof  as  the  mill,  but  in  a  room  so  distant  from  the  mill 
machinery  that  neither  tbe  millman  or  the  compressor  man  could  as- 
sist each  other.  If  the  compressor  is  placed  on  the  plate  floor,  a 
separate  room  should  be  provided  to  reduce  the  tendency  for  dust 
to  settle  on  the  compressor  and  in  the  moving  parts.  If  located  on 
the  concentrator  floor  it  is  generally  not  necessary  to  house  it  off, 
as  usually  very  little  dust  reaches  the  concentrator  floor. 

Mill  Management. — Each  5-stamp  battery  is  commonly  designated 
by  a  number,  but  it  is  better  to  use  letters  for  the  batteries,  reserving 
the  numbers  for  the  stamps  of  each  battery.  Thus  B4  is  a  short 


RECORDING  MILL  OPERATIONS  181 

way  of  designating  in  writing,  or  orally,  the  fourth  stamp  of  the 
second  battery. 

It  is  an  excellent  plan  to  paint  with  black  paint  a  space  upon  a 
battery-post  of  each  battery  for  use  as  a  blackboard.  Above  the 
board  is  painted  the  letter  or  number  of  the  battery.  Upon  the 
board  is  painted  in  white  the  words,  "Shoe,"  "Die,"  "Screen,"  and 
"Exam."  A  piece  of  chalk  is  kept  in  a  small  tin  box  nailed  at  the 
side  of  the  board,  and  the  day  and  month  on  which  the  shoe,  die, 
or  screen  is  renewed,  or  the  interior  of  the  mortar  is  examined,  is 
written  down.  Other  notes  or  instructions  are  placed  on  the  bottom 
of  the  blackboard.  Millmen  find  this  of  great  assistance  in  keeping 
track  of  mill  conditions. 

For  recording  the  loss  of  running  time  the  'stamp-hour'  system 
is  the  simplest  and  best.  In  this  system  the  length  of  time  any 
number  of  stamps  is  hung  up  is  multiplied  by  the  number  of  these 
stamps,  the  result  being  called  'stamp-hours.'  The  idea  is  to  show 
the  time  lost  as  measured  on  one  stamp  only,  and  to  simplify  the 
recording  of  lost  time.  Thus,  on  one  shift  a  single  battery  is  shut 
down  for  20  minutes,  which  is  equivalent  to  one  stamp  being  shut 
down  for  100  minutes  or  1%  stamp-hours ;  later  on  10  stamps  may  be 
shut  down  for  30  minutes,  making  a  loss  of  5  stamp-hours,  or  a  total 
of  6%  for  the  shift.  At  the  end  of  the  day,  or  month,  the  millman 
divides  the  total  number  of  stamp-hours  lost  by  the  number  of 
stamps  in  the  mill,  and  the  result  is  equivalent  to  the  number  of 
hours  of  running  time  lost  by  the  entire  mill. 

To  record  mill  work  various  report  systems  and  blanks  are  in 
use.  These  should  be  simple  and  cover  the  details  desired  without 
requiring  questions  from  the  management.  At  some  mills  a  tin 
holder  carrying  a  small  sheet  of  paper  is  nailed  to  the  post  of  each 
battery,  upon  which  all  hang-ups,  breakages,  and  other  causes  of 
stoppage  occurring  to  the  battery  are  noted.  These  papers  are 
collected  each  morning  by  the  mill  foreman  and  turned  into  the 
superintendent's  office.  An  excellent  method,  especially  in  a  small 
or  medium-size  mill,  is  to  post  a  form  covering  a  month  near  the 
change  room  of  the  mill.  This  form  is  on  heavy  detail  paper  and 
has  a  line  for  each  shift,  with  large  space  under  the  caption,  'Re- 
marks. '  Just  before  going  off  duty,  the  millman  whose  shift  is  end- 
ing fills  out  his  line,  and  under  'Remarks'  notes  down  what  stems 
have  broken,  where  new  steel  has  been  put  in,  what  boxes  are  run- 
ning hot,  and  any  other  details,  so  that  the  oncoming  millman,  by 
glancing  over  the  sheet,  will  note  at  once  what  has  been  done  on  the 
other  shifts  and  know  what  parts  of  the  mill  require  special  watch- 
ing. At  the  end  of  the  month  the  columns  are  totalled  for  the 


182  MILL   REPORTS 

monthly  report  of  operations  and  the  sheet  filed  away  as  a  summary 
of  the  work  for  the  month.  Where  there  is  irregularity  in  the  hours 
worked,  or  the  crew  is  large,  the  time-slip  method,  whereby  each  man 
turns  in  his  own  time,  should  be  used.  A  ruled  form  in  a  book,  or 
posted  on  the  wall,  should  be  provided  in  which  to  record  supplies 
received,  used,  and  remaining  on  hand  at  the  end  of  the  month. 
The  mill-foreman  should  be  provided  with  a  blank  form  in  which  he 
should  enter  daily  the  following  data,  if  it  can  be  consistently  done : 
Number  of  tons  crushed.  Ounces  of  mercury  fed  inside  the  bat- 
teries, on  outside  plates,  and  ounces  amalgam  collected  from  outside 
plates;  these  data  relating  to  feeding  of  silver  and  collection  of 
amalgam  should  be  entered  for  each  unit  of  5  stamps,  if  accurate 
information  is  desired.  Also  number  of  pounds  (wet  weight)  of 
sulphide  collected  from  concentrators  each  24  hours.  To  this  sheet 
may  properly  be  added  the  various  stoppages  and  their  cause,  such 
as  dressing  plates,  broken  belts,  babbitting  shafts,  changing  screens, 
broken  stems,  replacing  shoes  or  dies,  power  off,  and  the  numerous 
other  affairs  that  interfere  with  the  steady  operation  of  the  mill. 
This  sheet  is  not  posted  for  general  inspection,  but  goes  promptly 
each  morning  to  the  office  of  the  superintendent,  where  it  is  entered 
on  a  book  kept  for  the  purpose,  and  the  millsheet  placed  on  file. 

Another  sheet  should  show  the  supplies  consumed,  including  shoes, 
dies,  screens,  quicksilver,  lubricants,  light,  belting,  chemicals,  lum- 
ber, water,  power  (read  by  meter),  concentrator  belts,  and  all  other 
items  going  to  make  up  the  cost  of  milling,  including  labor. 

Whether  a  daily  mill  report  is  made  or  not  for  the  superintendent 
at  the  property,  or  the  manager  at  the  general  office,  a  monthly  sum- 
mary of  operations  should  always  be  required  of  the  mill  superin- 
tendent, which  should  include  a  cost-sheet,  and  also  a  description  of 
all  tests  and  experiments  made.  This  summary  should  be  exhaustive, 
giving  all  the  data  of  any  practical  value  it  is  possible  to  obtain,  and 
these  should  become  a  part  of  the  permanent  records  at  the  property, 
with  a  duplicate  at  the  general  office.  In  the  preparation  of  this  re- 
port the  millman  will  observe  many  things  of  interest  and  value  that 
may  result  in  further  study  and  increased  efficiency.  It  would  re- 
quire too  great  a  length  to  speak  of  the  invaluable  uses  these  reports 
are  put  to.  A  concrete  illustration  will  suffice.  A  small  mill  having 
a  somewhat  complicated  treatment  system  was  operated  for  an  ex- 
tended period  by  different  metallurgists  of  repute.  The  mill  finally 
shut  down  pending  negotiations  for  equipping  the  property  with  a 
larger  plant,  and  the  blocking  out  of  ore.  When  it  was  decided  to 
begin  metallurgical  operations  on  an  increased  scale,  the  company 
in  attempting  to  decide  whether  to  increase  the  small  plant,  build 


DETAILS   OP   MILL    CONSTRUCTION  .     183 

a  larger  mill,  or  use  some  other  system  for  treating  the  ore,  found 
itself  with  only  a  lot  of  scattered  incomplete  information  of  the  most 
vague  nature,  much  of  which  was  hearsay.  In  this  extremity  they 
were  obliged  to  send  out  a  metallurgist  to  start  up  the  small  plant 
and  by  a  series  of  experiments  determine  what  could  be  done — in 
short,  to  get  the  data  that  a  proper  report  system  should  have  given. 

The  general  superintendent,  or  manager,  can  materially  assist 
milling  operations  by  impressing  on  the  mine  foreman  the  necessity 
for  keeping  the  mill  bins  full ;  by  keeping  the  mine  foreman,  the  mill 
foreman,  the  cyanide  man,  and  the  assayer  in  harmonious  relation 
instead  of  antagonistic  to  each  other,  as  is  too  often  the  case;  and 
by  urging  the  mill  foreman  to  take  advantage  of  the  help  of  the 
assayer  in  his  testing. 

Directly  in  front  of  the  middle  of  the  batteries  a  floor  should  be 
erected  overhanging  the  concentrator  floor.  A  good  stove  should 
be  placed  here,  that  the  batteryman  on  the  night  shift  may  be  able 
to  warm  himself  at  a  point  where  he  has  everything  in  plain  sight, 
instead  of  going  out  to  the  boilers,  or  down  to  the  cyanide  plant.  In 
a  cold  climate  these  floors  have  been  boarded  up  to  form  a  clean  and 
cozy  change-room  with  a  glass  front.  The  clean-up  room  can  be 
situated  to  advantage  at  this  point.  It  is  preferable,  where  not  too 
cold,  to  surround  it  with  wire  netting  instead  of  boarding  it  up, 
that  there  may  be  more  light.  It  is  a  wise  expenditure  to  build  a 
commodious  and  well-equipped  clean-up  room.  Floors  should  be 
built  tight  and  drain  into  a  launder  running  the  length  of  the  mill 
to  a  box  from  which  the  amalgam,  sulphide,  and  sand  that  has  been 
flushed  into  it  can  be  recovered  to  go  into  the  clean-up  barrel  or 
through  the  mortars.  Concrete  floors  make  a  neat  looking  mill,  but 
are  cordially  detested  by  mill  employees  as  they  produce  leg-weari- 
ness, calloused  feet,  and  'draw  the  cold  and  dampness.'  A  mill- 
man  experiences  a  great  relief  in  changing  from  a  mill  having  con- 
crete floors  to  one  having  wood.  The  use  of  rubber  heels,  overshoes, 
or  thickly  soled  shoes  affords  some  relief.  Where  concrete  floors 
are  put  down,  a  walk  of  plank  or  grating  should  be  run  between  the 
concentrators  and  along  in  front  of  the  plates  and  at  other  conven- 
ient places  for  the  benefit  of  the  employees. 

A  work-bench  should  be  provided  together  with  a  full  set  of  the 
tools  such  as  are  required  in  a  stamp-mill,  including  the  more  com- 
mon carpenter  and  machinist  tools.  These  tools  should  be  stamped, 
but  not  kept  under  lock  and  key,  with  the  exception  of  the  extras. 
Each  tool  should  have  a  place  and  the  name  of  the  tool  should  be 
printed  at  that  place. '  During  shut-downs  on  account  of  lack  of 
power,  or  other  external  causes,  the  belts  should  be  gone  over  and 


184  SYSTEM  IN  MILL  OPERATION 

those  parts  of  the  mill  repaired  and  cleaned  that  cannot  be  con- 
veniently gotten  at  while  in  operation. 

The  millman  who  wishes  to  make  a  name  for  himself  will  keep  his 
mill  scrupulously  clean  and  neat  in  appearance.  He  will  first  stop 
the  running  out  and  splattering  about  of  oil  and  grease,  likewise  of 
the  water  and  pulp,  then  of  the  ore  that  falls  out  of  the  chutes,  and 
about  the  feeders.  Finally  he  will  remove  the  rust,  grease,  and  mud 
from  the  steins  and  shafts,  and  the  mortars.  Once  the  mill  is  bur- 
nished up  and  the  splattering  about  and  leakage  stopped  the  mill 
can  easily  be  kept  in  this  condition.  A  clean  mill  and  a  good  millman 
go  together.  There  is  a  great  difference  in  millmen,  some  are  so 
careless  and  inexpert  in  making  repairs  and  so  unsystematic  in  the 
daily  routine  work  that  the  duties  become  trying  to  the  employees. 
Other  millmen  are  able  to  keep  their  mills  in  such  good  condition 
and  to  plan  the  routine  of  daily  work  so  well  that  the  mill  work  is 
no  longer  odious  but  is  accompanied  with  a  considerable  degree  of 
gratification.  Besides  an  able  millman,  a  well  constructed  and  prop- 
erly designed  mill  is  necessary.  With  these  factors  the  stamp-mill 
becomes  the  most  satisfactory  metallurgical  machine  in  use,  to  those 
both  directly  and  indirectly  interested.  There  are  40-stamp  mills 
operating  without  a  machine  shop  or  even  a  lathe,  all  repairs  neces- 
sary being  made  by  the  millman  sometimes  assisted  by  the  black- 
smith. There  are  10-stamp  mills  that,  figuratively  speaking,  are  in 
the  machine-shop  all  the  time,  due  to  the  absence  of  one  of  these 
factors,  usually  to  defects  in  the  installation. 

No  whistling  or  shouting  should  be  allowed  in  a  mill,  except  as  a 
danger  signal.  To  call  attention  a  hissing  noise  should  be  made ;  as 
such  a  noise  is  keyed  in  a  different  pitch  from  that  of  the  stamps,  it 
can  be  heard  across  a  large  mill.  Similarly,  in  talking  no  attempt 
should  be  made  to  talk  above  the  roar,  but  in  a  moderate  tone  keyed 
in  a  different  pitch,  which  can  only  be  learned  by  experimenting. 
Sign  language  should  be  developed  as  far  as  possible.  Where  it  is 
desired  to  call  a  man  at  a  distance,  as  at  the  rock-breaker  or  the 
cyanide  plant,  a  triangle,  such  as  is  in  common  use  at  mine  boarding- 
houses,  should  be  used.  In  some  mills  the  foreman  carries  a  police 
whistle  for  the  purpose  of  calling  men.  Colored  signal  lights  are 
used  for  telephones. 

There  is  a  serious  part  of  stamp-milling — the  loss  of  hearing.  A 
10  or  20-stamp  mill  is  not  hard  on  the  hearing,  but  the  larger  mills 
cause  the  majority  of  men  to  become  deaf  in  time.  To  save  the  ear 
drums  as  much  as  possible  and  reduce  the  distress  of  the  continuous 
noise,  wads  of  cotton,  wool,  or  waste  are  worn  in  the  ears.  These 
should  be  softened  with  clean  oil  such  as  olive  oil  or  vaseline,  that 


LOSS   OF   HEARING 


185 


they  may  not  inflame  the  ears.  Further  relief  can  be  obtained  by 
sealing  the  ears  up,  after  the  cotton,  with  a  soft  pliable  wax  or  stiff 
salve  that  can  be  moulded  into  place. 

Handling  Pulp  and  Tailing. — For  elevating  pulp  where  necessary 
the  tailing  wheel  is  used  in  large  installations,  though  other  methods 


—  c — < 

Sectional  Elevation  of  8  by  48-inch  Pump. 

FBENIEB    SPIRAL    PUMP. 

(Frenier  &  Son,  Rutland,  Vt.) 

are  considered  preferable.  As  these  wheels  are  costly  to  install  and 
the  cost  of  operating  remains  practically  the  same  whether  a  large  or 
small  quantity  of  pulp  is  to  be  elevated,  some  other  machine  is  used 
in  small  plants.  The  centrifugal  pump  is  too  costly  and  troublesome 
from  the  shell,  liners,  and  stuffing-box  of  the  pump  becoming  rapidly 


186  ELEVATING   WET   PULP 

worn  by  the  grit.  The  Frenier  sand-pump  has  been  found  very 
satisfactory.  Its  maximum  lift  is  about  20  ft.  in  a  practical  way,  and 
for  a  higher  lift  two  or  more  of  them  should  be  placed  tandem.  The 
wear  on  these  pumps  is  mainly  in  the  bearings,  the  grit  of  the  pulp 
giving  no  trouble.  They  have  to  be  stopped  for  a  period  of  10  min- 
utes every  2  to  4  weeks  to  allow  replacing  the  gland  with  one  that 
has  been  re-packed.  Experiments  have  been  made  with  an  air-lift 
pump.  These  cost  little  to  install  and  to  keep  in  repair,  but  their 
efficiency  is  low.  The  air-displacement  pump  is  now  being  used  in 
pumping  slimy  and  gritty  liquids  and  slush,  and  has  been  introduced 
for  pumping  thickened  pulp  into  filter-presses  against  a  high  head. 
This  pump  would  appear  to  solve  the  problem  of  a  cheap  and  effi- 
cient installation  for  elevating  wet  pulp  as  they  cost  but  slightly 
more  than  a  centrifugal  pump,  require  little  attention,  are  compact, 
have  high  efficiency,  and  the  cost  for  wearing  parts  or  repairs  is 
nominal.  The  hydraulic  lift,  or  elevator,  is  being  used  for  elevating 
pulp  where  the  extra  amount  of  water  necessary  to  their  operation 
is  not  considered  undesirable,  as  in  a  canvas-plant. 

Stamp-mill  launders  within  the  mill  should  be  set  with  a  grade  of 
one  foot  in  twelve.  Discharge  launders  or  flumes  leading  away  from 
the  mill  should  have  a  grade  of  not  less  than  one  foot  in  sixteen.  A 
grade  of  one  foot  in  twenty  will  work  under  favorable  conditions 
without  giving  trouble,  but  is  generally  too  small,  particularly  in  a 
cold  country.  In  one  case  the  finely  crushed  tailing  of  a  40-stamp 
mill  was  transported  in  a  flume  having  a  grade  of  one  foot  in 
thirty-two,  but  considerable  trouble  was  experienced. 

Where  it  is  necessary  to  impound  the  tailing,  it  is  usually  done 
to  prevent  it  from  reaching  sites  or  water  courses  where  it  is  not 
wanted,  or  for  the  purpose  of  subsequent  treatment,  such  as  by  the 
cyanide  process.  A  hillside  can  usually  be  had  to  form  a  wall  on 
from  one  to  three  sides,  while  the  pond  is  laid  out  in  two  or  more 
sections  that  the  walls  of  one  section  may  be  raised  by  shoveling  or 
scraping  while  the  other  is  filling.  Where  the  tailing  is  not  being 
banked  for  future  treatment,  the  tailing  flume  is  carried  over  the 
pond  just  inside  of  the  wall  that  has  to  be  raised  by  shoveling.  The 
tailing  is  discharged  along  this  wall  through  several  small  gates. 
The  coarser  sand  of  the  tailing  settles  at  this  point,  damming  the 
slime  back  against  the  hillside  where  a  box  flume  laid  on  the  ground 
and  passing  underneath  the  pv  nd,  carries  off  the  clearer  water.  The 
depth  of  the  slime  is  increased  by  extending  the  bedrock  flume  as 
needed.  The  mill  flume  can  run  along  the  contour  of  the  hill  and 
small  V-shaped  troughs  can  be  lightly  trestled  up  to  carry  the  tail- 


TAILING  POND 


187 


ing  to  the  outer  bank  of  the  pond.  This  method  of  filling  results  in 
the  slime  being  separated  from  the  sand,  and  should  not  be  used 
where  the  tailing  is  to  be  eventually  cyanided,  as  it  is  impossible 
to  treat  this  caked  slime  without  a  highly  expensive  equipment.  In 
this  case  four  sets  of  inlets  and  outlets  should  be  spaced  about  each 
section  of  the  pond  and  a  change  made  from  one  set  to  another  daily 
or  semi-daily.  This  will  result  in  throwing  a  layer  of  sand  upon  a 
stratum  of  slime  through  which  it  will  sink  to  some  extent,  and  will 
enable  the  cyanide  man  to  put  a  homogeneous  and  leachable  charge 
into  his  vats  without  leaving  any  material  behind  as  unleachable. 


Cross  Section 


BUILDING    UP    A    TAILING   POND. 


These  ponds  have  been  used  to  return  some  of  the  water  to  the 
mill  for  re-use,  but  a  settling  plant  is  much  better.  This  may  be  of 
the  well  known  cone  settlers  purchased  outright  or  home-made  of 
wood  at  a  small  plant.  A  simple  and  efficient  water-saving  plant 
consists  of  deep  pulp-thickening  tanks  ending  in  cones  with  60° 
sides  and  large  gate-valve  discharges.  The  pulp  is  introduced  into 
the  centre  of  the  tank  some  distance  below  the  surface  of  the  over- 
flowing water  that  its  introduction  may  not  be  violent  and  that  the 
settling  effect  of  a  slowly  ascending  column  of  water  may  be  ob- 
tained. The  valves  are  opened  at  intervals  of  a  few  hours  to  with- 
draw a  part  of  the  thickened  pulp,  which  comes  out  as  a  thick  and 
solid  sludge  requiring  a  launder  set  at  heavy  grade.  The  wooden- 
box  settlers  so  common  around  small  mills  in  desert  regions  and  so 
unsatisfactory  in  operation,  should  be  divided  into  compartments 
fitted  with  these  cone  bottoms  and  gate-valves. 

Novel  instances  of  mill-tailing  put  to  agricultural  purposes  are 
found  in  California.  Some  30  years  ago,  the  tailing  from  a  large 
mill  crushing  a  quartz  ore  containing  much  of  the  slate  in  which  the 
orebody  lay,  after  running  in  a  creek  for  three  miles,  was  diverted  by 
an  earth  dam  and  impounded  to  form  a  fill.  The  flat  bottom  of  the 


188  TAILING-POND   FARM 

creek  had  been  cleaned  bare  years  before  by  placer  miners.  A  stone 
wall,  6  to  15  ft.  high,  was  roughly  laid  at  the  side  of  the  creek,  to 
raise  the  proposed  surface  above  high  water.  This  wall  was  about 
2200  ft.  long;  and  inclosed  a  strip  of  ground  of  that  length  and  from 
125  to  250  ft.  wide,  to  be  filled  by  the  tailing.  This  filling  was  done 
in  sections  and  required  several  years  to  complete.  The  surface  was 
well  manured,  and  the  tailing  was  found  to  make  an  excellent  soil 
for  growing  vegetables  and  fruits,  being  preferred  to  the  natural 
soil.  It  is  still  actively  worked  and  is  considered  the  best  garden 
in  the  county.  There  are  many  gardens  of  this  character  along  the 
Mother  Lode  of  California. 


PART  IV 

ARRANGEMENT  AND  CONSTRUCTION 
COSTS  OF  STAMP- MILLS 


By  CHARLES  T.  HUTCHINSON 


CHAPTER  XI 

ARRANGEMENT  OF  STAMP  BATTERY — LIGHT  AND  HEAVY  STAMPS — SEO 
TIONALIZED  MACHINERY JAW  AND  GYRATORY  CRUSHERS — PUR- 
CHASING A  MILL — SELECTION  OF  MILLSITE — COST  OF  CONSTRUCT- 
ING STAMP-MILLS. 

Arrangement  of  Stamp  Battery. — The  arrangement  of  stamp  bat- 
teries affects  first  cost  primarily,  and  to  a  certain  extent  the 
operating  cost.  Five  hypothetical  cases  will  be  given  to  illustrate 
this,  all  of  which  are  used  in  actual  practice.  It  will  be  assumed 
that  5-stamp  mortars  will  be  used;  that  the  battery-frame  will  be 
of  the  back-knee  type ;  that  the  drive  is  accomplished  by  means  of 
a  belt-tightener  and  countershaft  set  on  the  line  sills  below  the 
feeder  floor;  that  the  speed  of  the  countershaft  is  100  r.p.m.,  and 
that  of  camshaft  is  50  r.p.m.;  that  the  section  of  the  countershaft 
with  pulley  for  receiving  power  from  the  prime  mover  is  omitted ; 
and  that  no  battery-frames  are  included.  Figures  and  other  com- 
parisons are  made  on  the  basis  of  20-stamp  mills  having  1000-lb. 
stamps. 

Case  No.  1. — This  arrangement  includes  four  5-stamp  batteries 
individually  driven.  Each  battery  is  placed  in  a  2-post  frame,  and 
each  frame  is  set  4  ft.  apart.  As  shown,  a  floor  space  43  ft.  wide 
is  required  for  this  setting.  Easy  access  to  the  feeders  from  any 
part  of  the  plate  floor  is  possible  through  the  passageways.  This 
design  enables  the  mill  bins  to  be  of  large  capacity. 

Case  No.  2. — This  is  similar  to  Case  No.  1  in  that  the  batteries  are 
still  arranged  in  individually  driven  5-stamp  units,  but  each  10 
stamps  is  set  in  a  3-post  frame.  For  this  arrangement,  the  ends 
of  the  5-stamp  camshafts  butt  together  at  a  double-bearing  placed 
on  the  centre  post.  The  accessibility  of  Case  No.  1  is  practically 
preserved,  while  a  floor  space  only  35  ft.  long  is  required  as-  com- 
pared with  43  ft.  in  Case  No.  1.  The  shortening  of  the  floor  space 
brings  about  a  corresponding  decrease  in  the  cost  of  machinery, 
foundations,  and  the  mill  building.  This  is  a  very  practical  ar- 
rangement. The  illustration  of  the  Aurora  Consolidated  mill  on  page 
96  shows  a  battery  arranged  in  this  manner. 

191 


192 


a G 


CASE      NO. 


CASE      NO.  3 


El 


CASE    NO.  4 


PLn                                                           •"•                                                    P^ 

" 

1  •  •••• 

1 

i  *****  n  —  • 

U" 

•  £'-  • 

/'-  £'-  2'- 

•  ^i'  •/'- 

-^-m 

CASE     NO.  5 

STAMP-BATTEBY    ARRANGEMENT. 


ARRANGEMENT   OF   STAMP   BATTERY  193 

Case  No.  3. — This  arrangement  contemplates  the  erection  of  the 
mill  in  two  10-stamp  units.  Each  unit  of  10  stamps  is  set  in  a 
4-post  frame,  and  is  operated  with  a  single  camshaft,  the  battery 
pulley  being  placed  at  the  centre  of  the  camshaft.  The  floor  space 
occupied  is  38  ft.  long,  or  slightly  in  excess  of  that  required  for 
Case  No.  2.  The  battery  countershaft,  however,  is  shorter,  and  as 
there  are  two  less  drives  than  required  for  either  Cases  No.  1  or  2, 
the  cost  of  machinery  is  correspondingly  less.  This  form  of  con- 
struction will  insure  a  rigid  camshaft,  whose  ends  will  not  jump 
and  pound  in  the  bearing  boxes.  But  serious  difficulty  is  encoun- 
tered, as  the  shaft  must  sometimes  be  removed  from  its  boxes, 
when  the  battery  pulley  is  to  be  repaired  or  it  has  become  loose. 
However,  battery  pulleys  give  little  trouble  from  coming  loose  when 
self-tightening  clips,  similar  to  those  for  cams,  are  in  use.  The 
Nevada  Hills  mill,  illustrated  on  page  115,  is  arranged  in  this 
manner. 

Case  No.  4. — This  arrangement  embodies  10-stamp  units,  having  10 
stamps  operated  by  each  camshaft,  similar  to  Case  No.  3.  But  each 
10-stamp  battery  or  unit  is  erected  in  a  3-post  frame  with  a  space 
of  approximately  4  ft.  6  in.  in  the  clear  between  the  units.  Also, 
the  battery  pulley  is  placed  at  the  end  of  the  camshaft.  This  ar- 
rangement requires  a  floor  space  32  ft.  long,  which  is  considerably 
less  than  in  any  of  the  first  three  cases.  While  the  same  number  of 
drives  is  required  as  for  Case  No.  3,  the  battery  countershaft  is 
shorter,  thereby  decreasing  the  first  cost  of  machinery,  as  well  as 
that  of  foundations  and  mill  building.  The  Goldfield  Consolidated 
mill,  as  illustrated  on  page  121,  is  arranged  in  this  manner. 

Case  No.  5. — For  a  20-stamp  mill  this  is  the  cheapest  possible  ar- 
rangement from  a  standpoint  of  first  cost.  The  entire  20  stamps  are 
erected  in  a  5-post  frame,  and  in  two  10-stamp  units  whereby  10 
stamps  are  driven  from  each  camshaft.  The  ends  of  the  two  cam- 
shafts butt  together  at  the  centre  post  in  a  double-bearing.  A  floor 
space  only  26  ft.  wide  is  required.  This  type  of  battery  arrangement 
is  shown  in  the  illustration  of  the  North  Star  mill  on  page  117., 

The  following  tabulation  shows  the  relative  floor  spaces,  weights 
of  machinery,  and  approximate  costs  at  factory  of  each  of  these 
five  cases. 

Cost. 
$5482.00 
5384.00 
4943.00 
4791.00 
4823.00 


Case  No. 
1 

Floor  space,  ft. 
.      43 

Weight,  Ib. 

82  672 

2    

35 

81,667 

3    

38 

75,162 

4 

32 

73  415 

5    . 

26 

73,640 

194  MAKING   THE   CAMSHAFT 

It  will  be  noted  that  Case  No.  4,  although  taking  up  more  floor 
space,  is  cheaper,  as  far  as  the  first  cost  of  machinery  is  concerned, 
than  Case  No.  5.  The  reason  for  this  lies  in  the  position  of  the 
drives,  which  makes  possible  a  cheaper  counter-shaft.  On  the  other 
hand,  this  difference  will  be  more  than  counteracted  by  the  increased 
cost  of  the  mill  building.  The  cost  of  foundation  and  mill  building 
will  vary  directly  as  the  floor  space  increases. 

There  are  many  points  in  favor  of  Case  No.  2  from  the  standpoint 
of  operating  costs  because  of  the  nature  of  camshafts.  The  most 
frequent  cause  of  prolonged  breakdowns  in  stamp-mills  is  break- 
ages of  camshafts.  It  is,  of  course,  perfectly  feasible  to  devise  a 
camshaft  of  such  size  and  quality  of  material  as  will  make  it  wear 
indefinitely.  The  obstacle  in  the  way  of  this  is  the  purchase  of  mills 
on  purely  a  price-competition  basis.  The  stock  mill  of  1000-lb. 
stamps,  as  ordinarily  put  out  by  manufacturers,  has  a  camshaft 
5%  in.  diameter  and  about  14  ft.  2  in  long  where  10  cams  are 
mounted  on  a  single  shaft,  and  8  ft.  long  where  5  cams  are 
mounted  on  a  single  shaft.  The  material  used  in  most  cases  is  a 
so-called  mild  steel  that  has  preferably  been  drawn  under  the  ham- 
mer from  a  bloom  about  8  in.  square.  This  forging  process  has  two 
objects.  The  heating  helps  to  anneal  the  material  and  relieves  in- 
ternal stresses.  The  hammering  has  the  effect  of  compacting  the 
material  and  making  it  more  homogeneous  in  general.  On  the 
other  hand,  in  order  to  save  money  in  the  cost  of  manufacture,  some 
of  the  so-called  hammered  shafts  are  merely  rolled  shafts  that  come 
to  the  manufacturer  6  inches  in  diameter  direct  from  the  mill.  They 
are  not  intended  for  camshafts,  and  are  totally  unsuited  to  the 
severe  duty  that  is  exacted.  To  turn  such  a  rolled  shaft  to  the  re- 
quired diameter,  only  T^  in.  of  stock  has  to  be  turned  off  all  around. 
This,  in  some  cases,  is  barely  sufficient  to  clean  up  the  shaft  and 
present  a  bright  surface,  especially  if  the  shaft  has  not  been  care- 
fully straightened  before  being  put  into  the  lathe.  Again,  manu- 
facturers frequently  draw  a  5%-m-  shaft  from  a  6  or  6^-in.  square 
bloom,  the  object  being  to  reduce  the  cost  of  forging.  It  is  obvious 
that  a  reduction  in  the  amount  of  hammering  required  gives  a  cor- 
respondingly less  chance  to  secure  a  camshaft  that  is  homogeneous 
throughout.  These  matters,  of  course,  are  not  apparent  upon  in- 
spection of  the  finished  shaft,  and  buyers  seldom  appreciate  the  sig- 
nificance of  these  details  until  after  the  mill  is  placed  in  operation. 

Breakages  of  camshafts  are  due  primarily  to  crystallization  in- 
duced by  what  steel  makers  call  'fatigue.'  It  is  analogous  to  the 
fatigue  and  physical  breakdown  of  the  human  body,  for  the  shaft 


CAMSHAFT   BREAKAGE        •  195 

under  continual  hammering  while  in  use  gradually  changes  from  its 
fibrous  structure  to  a  crystalline  one  that  finally  succumbs  to  the  jar 
and  vibration  and  impact  to  which  the  camshaft  is  subjected.  Manu- 
facturers and  millmen  concede  that  broken  camshafts  are  bound  to 
occur,  and  so  the  object  of  the  mill  designer  is  to  make  these  break- 
ages as  few  as  possible,  and  to  arrange  the  mill  so  that  when  a 
breakage  does  occur,  as  small  a  portion  of  the  mill  as  possible  will 
have  to  be  shut  down. 

This  is  one  of  the  principal  reasons  for  advocating  that  each  5- 
stamp  battery  should  be  driven  by  its  own  camshaft.  If  a  camshaft 
breaks,  but  5  stamps  are  out  of  commission  instead  of  10  when  using 
10-stamp  camshafts,  while  the  cost  of  a  new  shaft  will  be  much  less 
for  5  stamps  than  for  10  stamps.  It  must  be  admitted  that  the  load 
on  a  10-stamp  shaft  from  a  standpoint  of  flexure  is  better  distributed 
than  on  a  5-stamp  shaft,  for  the  reason  that  the  intervals  in  revolu- 
tion are  one-twentieth  of  the  complete  circles  instead  of  one-tenth. 
It  must  also  be  admitted  that  the  5-stamp  shaft  is  not  as  well  anchor- 
ed in  the  bearings  as  the  10-stamp  shaft,  because  of  the  downward 
pull  of  the  driving  belt,  which,  for  so  short  a  shaft,  causes  the  shaft 
to  jump  more  at  the  farther  end.  To  reduce  this  tendency,  which 
is  a  material  cause  of  shafts  crystallizing  and  breaking,  it  is  advisa- 
ble to  confine  the  outer  end  of  the  shaft  by  means  of  a  capped  box  in- 
stead of  the  usual  open-pattern  box.  On  the  other  hand,  the  torsional 
strain  increases  directly  with  the  length  of  the  shaft  and  the  power 
to  be  transmitted,  while  the  10-stamp  shaft  is  subject  to  twice  the 
jar  and  vibration  due  to  cam  impact.  Not  only  that,  but  the  10- 
stamp  shaft  is  under  a  much  heavier  strain  where,  through  defective 
construction  or  abnormal  wear  or  lack  of  care,  the  bearing  boxes  do 
not  truly  and  rigidly  support  the  camshaft  or  one  of  the  three  boxes 
does  not  support  the  shaft  at  all.  Crystallization  is  rapidly  induced 
by  these  conditions  and  under  heavy  strain  the  shaft  may  break. 

Light  and  Heavy  Stamps. — The  four  important  questions  in  com- 
paring light  and  heavy  stamps  are:  (1)  will  the  heavy  stamp  work 
as  satisfactorily  as  the  light  stamp,  particularly  in  crushing  ore  to  a 
fine  mesh ;  (2)  what  economy  in  the  operating  costs  will  be  effected 
by  heavy  stamps;  (3)  what  reduction  will  be  effected  by  heavy 
stamps  in  the  costs  of  installation,  referring  to  excavations,  grading, 
foundations,  and  building ;  (4)  what  are  the  comparative  costs  of 
the  machinery  of  light  and  heavy  stamps.  Only  the  last  question 
will  be  discussed  herein.  The  subject  may  best  be  treated  by  the 
following  three  hypothetical  cases  of  reduction  works  crushing 
quartz  ore  to  pass  a  30-mesh  screen,  and  having  a  capacity  of  200 


196  LIGHT   AND   HEAVY   STAMPS 

tons  daily:  Case  A,  a  40-stamp  mill  of  1000-lb.  stamps,  preceded 
by  the  usual  breaking  plant.  Case  B,  a  10-stamp  mill  of  2000-lb. 
stamps,  preceded  by  the  usual  breaking  plant,  and  followed  by  a 
Dorr  mechanical  classifier  from  which  the  oversize  or  coarse  sand  is 
fed  into  two  Chilean  mills  for  regrinding.  Case  C,  a  20-stamp  mill 
of  2000-lb.  stamps,  preceded  by  a  breaking  plant  as  in  B. 

CASE  A. — FORTY  lOOO-Le.  STAMPS. 

Weight,  Ib.      Cost. 

One  breaking  plant,  including  grizzly;  12  by  20-in.  Blake 
crusher;  16-in.  troughing  belt-conveyor,  60-ft.  centres, 
with  automatic  tripper.  (Power  required,  20  hp.) 30,000  $  2,750 

One  40-stamp  mill,  including  four  10-stamp  batteries 
having  1000-lb.  stamps;  eight  ore-bin  gates;  eight  auto- 
matic feeders;  one  battery  trolley,  including  a  2-ton 
chain-block  and  70  ft.  of  6-in.  I-beam  track 185,000  11,000 

One  battery  countershaft,  including  belting,  pulleys,  bear- 
ings, and  four  battery-belt  tighteners.  (Power  requir- 
ed, 100  hp.  Floor  space,  77  ft.  wide) 12,500  1,250 


Total    227,500          $15,000 

CASE  B. — TWENTY  2000-Le.  STAMPS  AND  Two  CHILEAN  MILLS. 

One  breaking  plant  same  as  for  Case  A,  except  that  belt 

conveyor  and  automatic  tripper  are  omitted 21,000  1,500 

One  10-stamp  mill,  including  two  5-stamp  batteries  having 
2000-lb.  stamps;  two  ore-bin  gates;  two  automatic  feed- 
ers; one  5-ton  chain  hoist  with  trolley  and  30  ft.  of 
18-in.  I-beam  track;  one  Dorr  duplex  mechanical  classi- 
fier; two  6-ft.  Chilean  mills 190,000  14,750 

One  set  transmission  machinery,  including  battery  and 
Chilean  mill  countershafting,  with  belting,  pulleys, 
tighteners,  and  boxes  complete.  (Power  required,  120 
hp.  Floor  space,  20  ft.  wide  and  two  benches.) 12,000  1,450 


Total    223,000          $17,700 

CASE  C. — TWENTY  2000-Ls.  STAMPS. 

One  breaking  plant,  same  as  for  Case  A,  except  that  belt 

conveyor  and  automatic  tripper  are  omitted 21,000  1,500 

One  20-stamp  mill,  including  four  5-stamp  batteries  hav- 
ing 2000-lb.  stamps;  four  ore-bin  gates;  four  automatic 
feeders;  one  5-ton  chain  hoist  with  trolley  and  50  ft.,  of 
18-in.  I-beam  track  160,000  9,500 

One  battery  countershaft,  including  belting,  pulleys,  bear- 
ings, and  four  battery-belt  tighteners.  (Power  requir- 
ed, 100  hp.  Floor  space,  40  ft.  wide.) 13,500  1,350 


Total 194,500          $12,350 


LIGHT   AND   HEAVY   STAMPS  197 

The  question  will  be  asked,  why  does  the  cost  of  twenty  2000-lb. 
stamps  so  closely  approach  that  of  forty  1000-lb.  stamps?  It  is  be- 
cause the  heavier  pieces  must  be  made  of  larger  forgings  composed 
of  better  material,  which  costs  more  per  pound.  Also,  the  cost  of 
the  machine  work  on  the  larger  pieces  is  sufficiently  greater  to  make 
the  cost  of  the  machine  work  per  pound  equal  to  that  upon  lighter 
parts.  A  further  reason  for  the  increased  cost  of  heavy  stamps  in 
the  above  cases  is  that  the  diameter  of  the  shoes  has  been  increased 
from  the  usual  9-in.  diameter  with  1000-lb.  stamps  to  12  in.,  and  the 
length  of  the  mortars  and  camshafts  has  been  increased  accord- 
ingly. It  will  be  noted  that  this  is  an  increase  of  three-fourths  in 
crushing  area  to  keep  pace  with  the  doubling  of  the  weight  of  the 
stamp,  though  the  South  African  practice  with  1800  to  2000-lb. 
stamps  is  to  use  a  shoe  of  914-in.  diameter.  It  will  be  observed  that 
the  cost  of  the  'stamp-mill'  parts  in  both  the  light  and  heavy  stamps 
is  about  six  cents  per  pound. 

The  cost  of  the  heavy-stamp  and  Chilean-mill  plant  is  about  18 
per  cent  greater  than  that  of  the  light-stamp  (1000-lb.)  plant,  not- 
withstanding that  the  weight  is  2  per  cent  less.  This  is  due  in  part 
to  the  higher  cost  of  heavy  stamps,  the  addition  of  a  mechanical 
classifier,  and  the  use  of  more  belts,  which  is  a  costly  item. 

It  is  apparent  that  so  far  as  the  cost  of  machinery  is  concerned, 
Case  A  (forty  1000-lb.  stamps)  will  cost  211/2  per  cent  more  than 
Case  C  (twenty  2000-lb.  stamps),  while  Case  B  (stamps  and  Chilean 
mills)  will  cost  43%  per  cent  more  than  Case  C.  The  weight  of 
machinery  in  Case  A  is  17  per  cent  greater,  and  in  Case  B  is  14% 
per  cent  greater,  than  in  Case  C.  Therefore,  in  the  matter  of  the 
cost  of  machinery  and  freight  charges,  the  advantage  is  decidedly 
with  Case  C  (twenty  2000-lb.  stamps),  while  Case  A  (forty  1000-lb. 
stamps)  has  an  advantage  over  Case  B. 

Viewing  the  subject  from  the  cost  of  excavations,  foundations, 
and  mill  buildings,  the  difference  in  the  three  cases  becomes  very 
.pronounced.  The  forty  1000-lb.  stamps  will  occupy  a  floor  space  77 
ft.  in  width.  The  twenty  2000-lb.  stamps  will  occupy  a  floor  space 
40  ft.  in  width.  This  would  indicate  that  the  cost  of  the  excavation, 
foundation,  and  mill  building  for  the  light  stamps  would  approach 
twice  that  for  the  heavy  stamps.  The  combination  of  ten  stamps 
and  two  Chilean  mills  would  occupy  a  floor  space  only  20  ft.  wide, 
but  would  require  two  benches,  which  would  make  the  building 
costs  approach  that  of  the  twenty  2000-lb.  stamps. 

The  power  consumption  would  be  the  same  for  the  forty  1000-lb. 


198  MACHINERY   FOR    MOUNTAIN    PACKING 

stamps  or  the  twenty  2000-lb.  stamps,  but  would  increase  20  per 
cent  for  the  stamp-Chilean  mill  combination. 

Sectionalized  Machinery. — Mill  equipment  must  be  made  in  sec- 
tions when  destined  for  use  at  mines  in  remote  localities  where  road 
conditions  are  such  that  mule-back  transportation  is  necessary.  The 
weight  of  these  sections  is  necessarily  determined  by  the  carrying 
capacity  of  the  average  mule,  and  is  ordinarily  fixed  at  300  pounds. 
Wherever  possible  the  weight  limit  should  be  placed  at  half  this 
amount,  as  it  greatly  simplifies  proper  balancing  of  the  load  to  be 
able  to  put  a  150-lb.  section  on  each  side  of  the  mule's  back,  rather 
than  to  load  a  single  piece  weighing  300  pounds. 

The  necessity  for  sectionalizing  affects  three  essential  items : 
first  cost,  construction  or  assembling  cost,  and  design.  Of  the 
several  parts  of  a  stamp  battery,  the  following,  as  ordinarily  fur- 
nished, must  be  sectionalized : 

Mortar 
Stamp  stem 
Camshaft 
Battery  pulley 

All  of  the  other  parts  of  the  iron  work  come  within  the  section- 
alized  weight  limit. 

MORTAR. — The  mortar  is  perhaps  the  most  important  part  of  the 
battery,  therefore  design  and  quality  of  material,  rather  than  first 
cost,  should  govern  its  selection.  Badly  fitting  joints  soon  give 
way  under  the  continuous  hammering  to  which  the  mortar  is  sub- 
jected; crushed  ore  and  water  leak  out  carrying  with  them  particles 
of  quicksilver  and  amalgam ;  while  an  unstable  anvil  upon  which  the 
stamps  pound  promotes  breakage  of  stems  and  other  parts  and  di- 
minishes crushing  capacity.  Though  cast  iron  is  ordinarily  satis- 
factory for  solid  mortars,  a  combination  of  cast  and  plate  steel  for 
sectional  mortars  possesses  many  advantages.  Strength  and  dura- 
bility are  obviously  essential.  The  ideal  material  for  a  sectionalized 
stamp  mortar  (see  page  38)  combines  these  qualities  with  lightness. 
A  sectional  mortar  suitable  for  1000-lb.  stamps  and  made  with  a 
cast  iron  base  and  iVin.  steel  plate  sides  had  the  following  dimen- 
sions : 

Height  over  all   4  ft.  6      in. 

Length  over  all   : . . .   4  ft.  8%  in. 

Thickness  under  dies  7     in. 

Weight  finished  5000  Ib. 

A  similar  mortar  using  a  cast  steel  base  as  a  substitute  for  the 
cast  iron  would  only  requir*  a  thickness  of  6  in.  under  the  dies. 


SECTIONALIZED    MORTAR  199 

The  difference  in  weight  would  be  about  480  lb.,  a  point  not  to  be 
lightly  considered  when  the  high  cost  of  mountain  mule  packing 
is  taken  into  account. 

In  a  properly  designed  sectional  mortar,  the  base  sections  are 
carefully  machined,  grooved,  and  tenoned  in  order  to  secure  tight 
joints.  The  tenons  are  the  weakest  points,  being  subject  to  both 
shearing  and  bending  stresses.  Cast  iron  has  low  tensile  and  shear- 
ing strengths,  and  practically  no  elasticity.  The  comparative 
strength  of  cast  steel  may  be  taken  at  from  three  to  five  times  that 
of  cast  iron  in  these  respects.  The  mechanical  advantages  in  it? 
use  are  therefore  obvious. 

As  an  additional  precaution  to  insure  rigidity  in  the  mortar  base 
after  assembling,  two  bolts  are  inserted  longitudinally  through  all 
sections.  The  bolts  are  generally  made  1%  in.  diameter,  and  the 
holes  are  drilled  y1^  in.  larger  through  all  the  sections  after  they 
are  fitted  and  bolted  together.  When  assembling  the  mortar  on  the 
ground,  these  bolts  should  be  heated  to  a  dull  cherry  red  and  in- 
serted. The  nuts  should  be  tightened  with  a  monkey-wrench  and  not 
.by  two  men  on  the  end  of  a  long-handle  wrench.  The  latter  method 
will  result  in  either  stripping  the  threads  or  stretching  the  hot  bolts 
to  such  an  extent  that  in  cooling  the  mortar  may  crack. 

In  addition  to  the  through-bolts,  the  mortar  sections  have  the 
usual  flanged  joints  that  are  held  together  by  turned  bolts  carefully 
fitted  into  the  drilled  and  reamed  holes.  These  bolts  should  have  a 
moderate  drive  fit.  The  nuts  also  should  be  faced.  Careful  work- 
manship, accurate  fitting  of  all  joints,  and  thorough  rigidity  in  use 
should  characterize  the  well  designed  and  properly  built  section- 
alized  mortar.  Gasket  joints  for  this  purpose  are  an  abomination 
and  predestined  to  failure.  Flush-joint  mortar-base  sections,  unstif- 
fened  by  grooves  and  tenons,  place  all  the  strain  of  continuous 
pounding  upon  the  bolt  threads.  It  is  impossible  to  keep  the  flange 
bolts  tight,  even  by  riveting  over  the  nuts.  Small  leaks  mean  large 
losses,  and  a  dancing  mortar  is  not  conducive  to  rapid  crushing  or 
long  life  for  the  battery  parts.  The  difference  in  first  cost  varies 
with  the  types  of  construction,  but  is  so  small  an  item  as  to  be 
negligible  to  the  intelligent  buyer  when  the  interests  involved  are 
considered.  A  sectional  mortar  having  a  cast  steel  base  and  con- 
structed in  general  along  the  lines  described  above  would  cost  about 
$450,  or  $75  more  than  if  the  cast  iron  base  was  used.  The  difference 
in  weight,  however,  is  about  480  lb.,  so  it  will  be  seen,  when  the  cost 
of  freight  is  taken  into  consideration,  that  the  higher  cost  of  the 
steel  base  mortar  is  mor«  apparent  than  real. 


200  SECTIONALIZED   BOSSHEAD 

STAMP  STEM.— The  stem  for  a  battery  of  1000  Ib.  stamps  is  ordi- 
narily 3TV  in.  diameter,  15  ft.  long,  and  weighs  480  pounds.  This 
presents  a  most  awkward  problem  to  the  designer  of  sectionalized 
machinery.  The  excess  weight  is  180  Ib.,  and  the  length  is  such  that 
transportation  over  mountain  trails  is  both  difficult  and  costly.  The 
duty  of  the  stem  in  use  precludes  the  possibility  of  its  being  cut  in 
pieces.  This  situation  has  been  met,  without  impairing  the  crushing 
and  mechanical  efficiency  of  the  1000-lb.  stamp,  by  making  an  extra 
long  stamp-head  or  boss  in  two  pieces,  and  shortening  the  stem  to 


~8"- •• 14" 


165 Ib        200lb  174  I 

STAMP   FOB    SECTIONALIZED    MILL. 

provide  for  the  increased  weight  of  the  boss.  The  lower  half  of  the 
sectional  boss  has  the  usual  taper  recess  cored  to  receive  the  neck 
of  the  shoe.  At  the  upper  end  is  a  taper  shank  the  same  as  a  shoe 
neck.  This  shank  is  wedged  into  a  taper  recess  in  the  upper  half 
of  the  boss  in  precisely  the  same  manner  as  the  shoe  is  fastened 
to  the  boss  in  a  standard  batte^.  The  upper  end  of  the  top  section 
of  the  boss  is  bored  as  usual  for  the  taper  end  of  the  stem.  The  fol- 
lowing schedule  of  weights  shows  the  advantage  in  the  new  method 
over  the  old : 

Old  method.  New  method. 

Size,          Weight,  Size.          Weight, 

in.        ft.  Ib.  in.        ft.  Ib. 

Stem    3T^byl5  480  3^  by  11  350 

Tappet  9  by  13  125         9    by  13  125 

Boss    (solid)    9  by  17  234 

Boss  (sectional,  upper) 8£  by  14  174 

Boss  (sectional,  lower) 8i  by  14  200 

Shoe  9  by  8  166         9    by    8  166 

Total  1005  1015 

It  is  obvious  that  the  sectional  boss  should  under  no  circumstances 
be  made  of  cast  iron.  Chrome  cast  steel  makes  breakages  practically 
a  negligible  feature,  except  in  the  remote  possibility  of  a  casting 
proving  defective. 

CAMSHAFT. — This  portion  of  the  stamp  battery  has  thus  far  de- 
fied the  efforts  of  the  designer  at  successful  sectionalizing.  The  cam- 
shaft for  a  battery  having  1000-lb.  stamps  would,  if  made  of  ham- 
mered iron  or  so-called  mild  steel,  be  not  less  than  5%  in.  diameter, 
although  some  builders  make  them  5T7^  in.  diameter  for  batteries 


HOLLOW    CAMSHAFT  201 

in  5-stamp  units.  For  a  unit  of  this  size,  which  is  the  maximum  for 
a  sectionalized  mill,  the  length  may  be  taken  as  8  ft.  2  in.,  assuming 
12-in.  posts  5  ft.  apart.  A  shaft  57/$  in-  by  8  ft.  2  in.  weighs  about 
760  Ib.,  or  more  than  double  the  sectional  weight  limit. 

An  expedient  that  has  been  used  with  some  degree  of  success  has 
been  to  split  the  shaft  in  halves  longitudinally  and  dovetail  them 
together,  using  countersunk  head  machine  screws  to  hold  the  pieces 
together.  This  is  effective  in  reducing  the  weight  of  the  pieces,  but 
is  also  open  to  several  objections,  principal  of  which  is  the  danger 
of  springing  the  pieces  in  handling  en  route,  and  the  difficulty  in 
keeping  the  screws  tight  when  the  shaft  is  in  use.  The  jointed  shaft 
is  less  strong  to  a  degree  corresponding  to  the  tightness  of  the  joint, 
than  a  solid  shaft  of  the  same  diameter.  A  sectional  shaft  of  this 
size  costs  $75  more  than  a  one-piece  shaft,  and  it  is  questionable 
whether  the  extra  cost  is  justified  by  the  results  achieved. 

A  far  superior  method  is  to  use  a  hollow  shaft.  In  order  to  keep 
the  overall  dimensions  and  consequently  the  weight  down  these  hol- 
low shafts  must  be  made  of  the  very  best  materials  obtainable.  A 
number  of  shafts  were  made  to  the  following  specifications,  and  after 
several  years  of  service  are  still  unbroken:  "Camshafts  must  be 
made  of  the  best  mild  open-hearth  steel,  test  pieces  from  which  must 
exhibit  a  tensile  strength  of  not  less  than  60,000  nor  more  than 
70,000  Ib.  per  sq.  in.,  and  an  elongation  of  not  less  than  25%  in  4 
inches.  A  bar  1/2  in-  square  to  bend  cold  through  an  angle  of  180° 
around  a  mandrel  1  in.  diameter  without  showing  any  signs  of 
fracture.  The  camshafts  are  to  be  hollow,  5T7g-  in.  outside  by  8  'ft. 
long,  bored  cut  to  3V±  in-  diameter  inside ;  to  be  turned  full  length 
and  to  be  drilled  for  cam  fastenings  and  camshaft  pulleys."  This 
shaft  weighed  400  Ib.  finished,  and  cost  about  $175.  While  this  is 
considerably  in  excess  of  the  cost  of  either  the  solid  or  split  shafts, 
it  is  so  far  superior  for  the  purpose  that  there  should  be  no  question 
as  to  a  choice  whenever  conditions  demand  light  sectionalized  con- 
struction. 

BATTERY  PULLEY.— The  battery  pulley  as  ordinarily  furnished 
with  a  standard  5-stamp  mill  is  72  in.  diameter  and  13  in.  face.  It  is 
built  up  of  wood,  fitted  with  cast  iron  sleeve  flanges,  and  shipped 
completely  assembled,  weighing  about  1300  pounds.  It  is  not  dif- 
ficult to  ship  such  a  pulley  knocked  down.  The  wood  segments  are 
cut,  painted,  and  crated  in  packages  of  any  desired  weight.  The 
face  of  the  pulley  must  be  turned  true  at  the  mill  after  assembled, 
but  this  may  be  easily  done  when  it  has  been  placed  in  its  proper 
position  on  the  camshajit. 


202  SOLID  VS.  SECTIONAL-FRAME  CRUSHERS 

The  sleeve  flanges  as  ordinarily  furnished  are  made  in  two  pieces, 
one  with  a  hub  cast  on  and  one  without.  As  the  combined  weight  of 
a  set  of  36-in.  flanges  is  about  750  lb.,  it  is  necessary  to  make  the 
flanges  and  hub  separate  in  order  to  come  within  the  mule-pack 
weight  limit.  Again,  in  this  instance,  steel  may  be  substituted  for 
the  usual  cast  iron  to  great  advantage.  Excellent  results  have  been 
obtained  with  steel  flanges  30  in.  diameter,  and  used  on  a  wood  pulley 
66  in.  diameter  and  13  in.  face.  The  specification  used  was  as  fol- 
lows :  ' '  Camshaft  pulleys  66  in.  diameter  by  13  in.  face.  The  pulleys 
to  be  constructed  of  wood  with  cast  steel  sleeve  flanges.  The 
steel  flanges  to  be  secured  to  the  shaft  by  a  self-tightening  fastening 
similar  to  that  used  for  the  cams.  The  wood  segments  composing 
the  pulleys  to  be  carefully  fitted,  assembled,  and  bolted  together,  and 
to  be  knocked  down  for  shipment.  No  part  of  the  sleeve  flanges  to 
weigh  over  200  lb.  All  necessary  bolts  for  securing  the  wood  work 
to  the  flanges  to  be  supplied." 

The  sleeve  flanges  above  weighed  as  follows : 

Pounds. 

Two  flange  sections  320 

One  hub  145 

Total   . . . .  f 465 

They  cost  about  $85,  or  $35  more  than  the  ordinary  cast  iron.  The 
greater  facility  with  which  they  could  be  transported,  however,  more 
than  overcame  this  difference. 

Jaw  and  Gyratory  Crushers. — Rock  breakers  as  ordinarily  manu- 
factured may  be  broadly  classed  into  two  types,  the  Blake  or  oscil- 
lating jaw  type,  and  the  gyratory.  Blake  breakers  may  be  further 
subdivided  into  two  types.  One  is  constructed  with  sectional  frames 
tied  together  with  heavy  steel  tie-rods  which  take  the  strain  of  crush- 
ing and  are  in  tension.  The  other  is  made  with  a  solid  one-piece 
frame  in  which  the  sides  and  ends  of  the  breaker  are  cast  in  one 
piece.  There  is  a  good  reason,  within  certain  limits,  for  the  sectional- 
frame  construction.  Forged  steel  is  obviously  better  adapted  to 
withstand  a  tensile  strain  than  cast  iron,  as  the  latter  has  no  elas- 
ticity of  any  consequence  and  a  comparatively  low  tensile  strength 
per  unit  of  area.  In  order  to  manufacture  a  solid-frame  crusher 
that  will  render  satisfactory  service,  it  is  necessary  to  use  a  large 
factor  of  safety  in  designing  the  frame.  This  results  in  a  very  heavy 
crusher  which  is  difficult  of  transport,  and  which  is  expensive  to  re- 
pair in  case  of  failure  of  the  frame.  On  the  other  hand,  the  me- 
chanical difficulties  in  tying  the  end-frame  sections  together  and 
keeping  them  tight  and  rigid  greatly  increase  in  constructing  a 


DATA   UPON   CRUSHERS                                                203 

sectional-frame  type  of  crusher  beyond  certain  sizes.    Both  types  of 
crushers  are  illustrated  on  pages  15  and  16. 
With  the  gyratory  breakers  the  first  objection  is  the  high  first 

BLAKE  JAW 

CRUSHER 

t 

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Horse-power. 

1 

6  by  8 
7  by  10 
8  by  12 
10  by  16 
12  by  20 
14  by  24 
18  by  24 

4               2,700 
6               4,000 
8               5,500 
12             10,200 
20             16,600 
25             26,600 
35 

4,000 
8,000 

16,500 
25,000 
36,000 
54,000 

4 

7 
8 
13 
18 
24 
40 

2 

3 

4 

5 

6 

GYRATORY  CRUSHER 

6 

Receiving  openings, 
each,  inches. 

Combined  openings, 
inches. 

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if 

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Weight. 

I 

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o 

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5  by  20 

5  by  40 
6  by  48 
8  by  60 
9  by  70 
11  by  80 
12i  by  90 
15  by  110 
18  by  126 
21  by  152 
25  by  200 

4  to  8 
6  to  12 
10  to  20 
15  to  30 
30  to  50 
50  to  80 
70  to  120 
120  to  180 
140  to  220 
200  to  400 

7,500 
9,500 
15,500 
22,500 
35,000 
48,000 
71,500 
100,000 
160,000 
180,000 

6 
10 
16 
20 
25 
35 
55 
85 
120 
150 

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4 

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5 

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6   

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8   
9    
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15  by  55 
18  by  63 
21  by  76 
25  by  100 

204 


COMPARISONS   OF    CRUSHERS 


cost  for  the  small  sizes  as  compared  with  the  Blake  type.  The  second 
objection  is  the  contracted  feed  opening  in  proportion  to  tonnage- 
output  rating. 


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CURVE  No.  1.    FACTORY  COST  OF  CRUSHERS.    SIZES  IN  TERMS  OF  AREA  OF 

FEED   OPENING. 


Comparisons  of  first  cost  may  best  be  studied  by  means  of  curves. 
Curve  No.  1  shows  the  first  cost  at  the  factory  for  all  three  types 
of  machines.  The  ordinates  represent  the  area  of  the  feed  opening 
in  square  inches,  and  the  abscissae  represent  the  first  cost  in  dollars 
at  the  factory.  In  studying  these  curves  it  will  be  noted  that  the 
gyratory  crusher  is  by  far  the  cheapest  in  sizes  down  to  the  No.  3 
machine,  which  has  an  opening  of  8  by  30  in.  for  each  of  its  two 
feed  openings.  The  manufacturers  rate  this  machine  at  10  to  20 
tons  per  hour,  and  it  is  conceded  that  as  far  as  first  cost  is  con- 
cerned the  gyratory  breaker  cannot  compete  with  the  Blake  below 
this  size. 

A  further  reference  to  Curve  No.  1  will  show  the  curve  of  the 
solid-frame  Blake  machine  crossing  that  of  the  sectional-frame  ma- 
chine at  a  point  which  would  indicate  that  the  sectional-frame  ma- 
chine is  cheaper  in  first  cost  in  sizes  of  about  10  by  16  in.  and  smaller. 


CRUSHER  FOR  LARGE  ROCK 


205 


Beyond  this  point,  however,  the  advantage  lies  with  the  solid-frame 
machine.  It  is  admitted  that  the  most  satisfactory  basis  for  com- 
parison would  be  that  of  actual  tonnage  output,  but  as  this  varies 


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CURVE  No.  2.    FACTORY  COST  OF  CRUSHERS.    SIZES  IN  TERMS  OF  WIDTH  OF 
OPENING. 


so  widely  in  different  localities  and  as  it  is  obviously  most  difficult 
or  impossible  to  obtain  examples  where  all  three  types  of  machines 
may  be  operated  crushing  the  same  rock  under  exactly  the  same 
conditions,  this  basis  of  comparison  is  out  of  question.  The  manu- 
facturers' ratings  also  vary  widely — as  much  as  100%.  Nor  can  any 
comparison  that  is  not  misleading  be  made  between  jaw  and  gyra- 
tory crushers  by  means  of  area  of  feed  opening. 

The  object  of  installing  a  rock  breaker  is  to  avoid  doing  by  hand 
what  can  be  done  better  and  more  cheaply  by  machinery,  regardless 
of  the  theoretical  capacity  of  a  breaker  which  cannot  crush  a  rock 
that  is  too  large  to  permit  of  its  entering  the  feed  opening.  For  in- 
stance, the  No.  3  gyratory  mentioned  before  has  two  8  by  30  in.  feed 


206  SELECTION   OF    CRUSHER 

openings  or  feed-opening  dimensions  of  8  by  60  in.,  and  is  rated  at 
from  10  to  20  tons  per  hour.  The  area  of  each  of  the  two  openings, 
therefore,  is  240  square  inches.  To  obtain  an  equivalent  area  of  feed 
opening  in  the  Blake  type  machine  requires  one  with  an  opening  12 
by  20  in.,  which  is  rated  at  15  tons  per  hour.  A  piece  of  rock  larger 
than  an  8-in.  cube  would  not  be  taken  into  a  No.  3  gyratory,  while 
the  Blake  with  a  feed  opening  of  equivalent  area  would  take  a  rock 
up  to  a  12-in.  cube,  or  50  per  cent  greater  than  the  gyratory.  From 
this  standpoint  the  12  by  20-in.  Blake,  rated  at  15  tons  per  hour, 
would  be  the  equivalent  of  the  No.  6  gyratory  having  two  121/2  by 
45-in.  openings  and  rated  at  50  to  80  tons  per  hour. 

Curve  No.  2  compares  the  factory  cost  of  the  three  types  of 
crushing  machines  as  in  Curve  No.  1,  except  that  the  ordinates  rep- 
resent the  width  of  feed  opening  in  inches  instead  of  area  of  feed 
opening.  On  this  basis  of  comparison  the  situation  becomes  changed 
and  the  gyratory  will  be  seen  as  the  most  expensive.  The  solid- 
frame  Blake  crusher  curve  crosses  that  of  the  sectional-frame 
Blake  machine  at  the  12  by  20  in.  size,  thus  indicating  that  for 
smaller  sizes  the  sectional-frame  crusher  is  cheaper,  and  that  for  the 
larger  sizes  the  solid-frame  machine  has  the  advantage. 

The  entire  question  of  the  selection  of  a  crusher  is  an  economic 
one  and  the  true  basis  of  comparison  is  one  of  operating  costs,  rather 
than  factory  and  construction  costs.  It  is  the  concensus  of  opinion 
of  experienced  operators  that  replacements  and  renewals  may  be 
more  easily  and  more  cheaply  accomplished  with  the  Blake  than 
with  the  gyratory.  The  main  reason  for  the  installation  of  the 
gyratory  in  the  majority  of  crushing  plants  having  a  capacity  in 
excess  of  20  tons  per  hour  is  in  the  lower  first  cost,  and  the  fact  that 
the  average  run  of  mine  rock  at  many  mines  is  of  such  a  size  that 
nearly  the  whole  of  it  may  be  taken  into  a  feed  opening  8  in.  wide. 
Where  the  breaker  is  fed  by  hand,  the  comparatively  narrow  open- 
ing of  the  gyratory  may  not  greatly  influence  the  cost  of  rock 
breaking,  for  the  attendant  can  sledge  the  oversize  if  the  percentage 
is  not  too  great.  But  if  the  breaker  is  to  be  fed  automatically  and 
is  not  to  receive  continuous  attention,  it  is  of  the  utmost  importance 
to  install  a  breaker  with  a  feed  opening  wide  enough  to  receive  the 
largest  pieces  of  rock. 

Purchasing  a  Mill. — The  first  requisite  in  purchasing  a  mill  is  that 
the  buyer  should  know  what  he  wants.  Some  buyers  want  to  put 
up  a  mill  for  the  purpose  of  being  better  able  to  sell  stock  in  their 
mines,  and  so  want  as  cheap  a  mill  as  possible,  while  other  buyers 
want  a  mill  to  obtain  the  metals  from  their  ores,  and  so  want  as 


DESIGNING   THE   MILL  207 

efficient  a  mill  as  possible.  The  latter  must  comprehensively  sample 
their  orebodies  and  turn  the  samples  over  to  a  metallurgist  for 
testing  to  determine  the  proper  process.  This  is  one  of  the  critical 
stages  in  the  development  of  a  mine,  and  requires  scrupulous  care 
and  study.  It  is  essential  that  the  samples  shall  represent  the 
average  of  the  ore  to  be  milled.  If  a  pay  shoot  or  vein  is  but  12  in. 
wide,  it  is  foolish  to  sample  the  pay  shoot  only,  without  taking  into 
consideration  the  impossibility  of  mining  a  pay  shoot  of  that  width 
without  including  a  certain  amount  of  waste.  And  yet  this  is  done 
over  and  over  again.  Ores  that  will  'assay'  $8  to  $10  are  found  to 
'mill'  but  $2  to  $3,  so  that  the  disappointed  stockholders  shake  their 
heads  and  resolve  to  have  nothing  more  to  do  with  mining  invest- 
ments. The  sampling  should  be  performed  under  the  direction  of 
the  superintendent  or  mining  engineer  in  conjunction  with  the  metal- 
lurgist, for  the  first  two  should  know  the  grade  of  the  ore  and  what 
ore  it  is  expected  to  send  to  the  mill,  while  the  wide-awake  metallur- 
gist acquires  a  knowledge  of  the  nature  and  characteristics  of  the 
ore  and  the  proportions  of  the  different  kinds  of  ore  that  will  be 
supplied  to  the  mill,  and  can  call  attention  to  any  mistake  in  select- 
ing the  samples. 

After  the  samples  have  been  tested  by  the  metallurgist  and  the 
proper  treatment  system  and  machinery  outlined  by  him,  the  next 
step  is  the  designing  of  the  mill  and  the  purchase  of  the  apparatus. 
The  mill  should  be  designed  by  a  mechanical  engineer  who  has  spec- 
ialized in  this  line,  and  his  work  should  be  outlined  and  directed  by 
the  metallurgist.  The  metallurgist  is  a  man  who  has  worked  with 
the  process  in  many  fields,  and  has  an  up-to-date  and  working  knowl- 
edge of  the  appliances  that  may  be  used.  But,  generally  speaking, 
the  metallurgist  cannot  calculate  in  a  practical  way  the  strength 
of  materials,  or  determine  what  the  chords  of  a  roof  truss  should  be, 
or  the  proper  size  and  arrangements  of  the  driving  parts,  or  the 
proper  foundations  for  the  machinery,  etc.  Obviously  these  things 
are  the  work  of  the  mechanical  engineer,  who  is  a  specialist  in  them. 
And  the  closer  in  touch  that  the  metallurgist  and  the  mechanical 
engineer  work,  the  better  will  be  the  results.  The  final  work  of  de- 
signing consists  in  drawing  up  a  complete  list  of  specifications,  giv- 
ing the  quantities  and  sizes  of  the  different  parts  or  devices  required, 
and  particularly  specifying  their  material  and  methods  of  manu- 
facture. With  this  list  in  hand  the  buyer  knows  what  he  wants. 

However,  the  entire  question  of  building  a  mill  is  so  bound  up 
with  the  manufacturer  of  mill  machinery,  that  a  correct  under- 
standing of  his  functions  is  necessary.  The  machinery  manufacturer 


208  BUYING   THE   MILL 

lives  by  selling  machinery,  and  years  of  experience  have  taught  him 
that  he  must  proceed  along  certain  lines.  One  of  these  is  that  he 
must  keep  a  force  of  mechanical  engineers  and  designers,  and  sub- 
mit mill  designs  and  give  advice  to  prospective  buyers  free  of  charge. 
It  is  always  well  to  seek  the  advice  of  the  manufacturer,  as  much 
money  may  be  saved  by  using  his  standard  product  and  patterns 
wherever  they  may  be  found  applicable.  But  the  representatives  of 
the  buyer  should  be  the  men  who  draw  up  the  plans  and  specifica- 
tions, not  the  manufacturer,  for  the  manufacturer  cannot  assume  the 
responsibility  for  the  successful  operation  of  the  plant  in  addition  to 
his  own  responsibilities,  and  so  it  will  invariably  be  found  when  it 
comes  to  signing  a  contract  that  the  manufacturer  will  only  "guar- 
antee the  workmanship  and  material  to  be  free  from  defects  when 
used  for  the  purpose  ordered."  There  will  seldom  be  any  guarantee 
of  tonnage  output,  and  never  a  guarantee  of  any  degree  or  percent- 
age of  extraction ;  the  responsibility  for  the  mill 's  successful  opera- 
tion, outside  of  failure  due  to  defective  material  and  workmanship, 
rests  with  the  buyer  and  his  representatives. 

The  buyers  of  small  plants  seldom  appreciate  these  facts,  and 
in  order  to  economize  upon  the  cost  of  engineering  services,  will 
frequently  submit  their  own  general  ideas  as  to  the  proper  treat- 
ment to  the  machinery  manufacturer  in  order  to  obtain  advice  for 
nothing.  The  manufacturer  under  such  conditions  does  the  best 
he  can.  He  must,  perforce,  assume  the  buyer's  statement  of  con- 
ditions to  be  correct,  and  devise  a  plant  accordingly.  He  knows, 
of  course,  that  the  buyer  is  telling  the  same  story  to  other  manu- 
facturers and  that,  therefore,  there  is  no  chance  that  all  will  bid 
upon  a  uniform  set  of  specifications.  Each  manufacturer  bids  upon 
what  in  his  opinion  is  the  cheapest  plant  that  can  be  put  up.  He 
keeps  his  bid  as  low  as  possible,  partly  by  the  use  of  cheap  material 
and  a  scant  design,  and  mainly  by  eliminating  every  item  possible, 
even  the  most  necessary  accessories  are  often  omitted.  It  should 
be  clearly  understood  that  the  manufacturer  indulges  in  no  guess- 
work in  making  his  bid,  but  does  it  by  setting  down  each  item  of 
machinery  and  parts  that  he  will  supply  and  the  price  that  he  can 
sell  it  for,  and  then  obtaining  the  sum  total  of  the  items.  Obviously, 
the  more  items  he  can  eliminate,  the  lower  will  be  the  bid.  A  large 
majority  of  buyers  of  this  type  will  hastily  turn  over  the  pages  of 
the  specifications  until  they  come  to  the  last  page.  Then  scrutiniz- 
ing the  final  figures  or  lump-sum  bid,  will  wonder  why  A  can 
furnish  a  'complete'  mill  so  much  more  cheaply  than  B — and 
promptly  proceed  to  give  A  the  order.  The  eventual  result  is  that 


BUILDING   THE   MILL  209 

it  will  cost  the  buyer  from  15  to  50%  additional  for  extra  machinery 
and  accessories,  repairs  and  alterations,  and  the  loss  of  time  in  get- 
ting mill  fitted  up  and  into  commission  is  a  matter  of  even  more 
serious  consequence. 

This  type  of  buyer  is  a  severe  tax  on  the  conscience  of  the  manu- 
facturer, who  has  learned  to  recognize  the  type  on  sight  and  to 
act  accordingly.  He  also  knows  that  a  buyer  showing  so  little 
intelligence  in  buying  is  apt  to  have  shown  but  little  more  in  de- 
veloping his  mine,  and  that  the  mill  will  probably  not  operate  more 
than  six  months,  not  that  the  machinery  installed  is  inadequate  or 
defective,  but  that  the  buyer  has  neglected  to  provide  himself  with 
a  mine.  As  a  rule  machinery  manufacturers  are  honest,  but  pro- 
fessional mill  builders  recognize  that  great  dissatisfaction  arises 
in  putting  up  the  mills  of  certain  manufacturers,  while  workaday 
millmen  speak  of  the  mill  put  out  by  certain  manufacturers  as 
bunglesome  and  unsatisfactory  of  operation  because  of  poor 
material  and  bad  design.  All  of  which  tends  to  prove  that  a  mill 
should  be  purchased  on  merit  of  a  reputable  manufacturer. 

Having  purchased  the  mill,  the  next  step  is  its  erection  by  a  com- 
petent millwright  or  mill  erector,  who  should  work  in  conjunction 
with  the  metallurgist  or  millman  who  is  to  put  the  mill  into  commis- 
sion, at  least  the  assistance  of  the  millman  should  be  sought  as  the 
mill  nears  completion.  This  is  for  the  reason  that  the  millman  has 
certain  detailed  knowledge  which  can  hardly  be  expected  in  the 
erector  or  millwright,  also  because  there  are  a  great  many  small 
details  of  construction  and  arrangement  which  the  millman  requires 
to  satisfy  his  own  personal  ideas  and  which  he  will  make  sooner 
or  later. 

It  has  been  stated  that  a  metallurgist  or  metallurgical  engineer 
should  test  the  ore  and  outline  the  treatment  system  and  machinery. 
That  a  mechanical  engineer,  working  under  the  advice  of  the 
metallurgical  engineer  should  design  the  mill  and  draw  up  the 
specifications.  That  the  specifications  should  be  submitted  to  the 
manufacturers  for  bids  upon  each  item  of  the  quality  specified.  And 
finally,  that  the  mill  should  be  erected  by  a  millwright  or  mill 
erector  working  with  the  advice  of  the  millman  who  is  to  operate 
the  mill.  This  applies  admirably  to  mills  of  medium  and  large  size, 
but  by  far  the  greater  proportion  of  mills  vary  in  size  between 
2  and  20  stamps.  In  building  small  mills  embodying  only  standard- 
ized stamp-milling  and  concentration,  financial  and  other  conditions 
may  be  considered  not  to  warrant  such  extensive  engineering 
service.  In  such  cases  the  mill  plans  will  doubtlessly  be  furnished 


210  MILLSITE 

by  the  machinery  manufacturer,  but  the  plans  and  specifications 
should  be  checked  by  the  experienced  men  who  will  build  and 
operate  the  mill,  while  the  mill  should  be  purchased  on  merit  and 
individual  specifications  and  not  on  a  lump-sum  bid. 

Selection  of  Millsite. — The  first  step  to  be  taken  before  starting 
to  prepare  an  estimate  or  a  mill  plan  is  the  selection  of  a  site.  As 
the  mill  must  be  designed  to  suit  the  site,  which  influences  the  cost 
of  milling  as  well  as  construction,  a  brief  discussion  of  the  neces- 
sary characteristics  will  be  given.  It  is  recognized  that  the  position 
of  the  mine  and  the  method  of  treating  the  ore  are  fixed,  and  it  lies 
with  the  engineer  in  charge  of  the  proposed  mill  construction  to 
make  the  best  possible  use  of  existing  conditions  as  far  as  the 
selection  of  a  millsite  is  concerned.  As  the  influence  of  the  site 
upon  milling  costs  is  of  prime  importance,  the  characteristics  of  an 
ideal  site  from  this  standpoint  will  be  considered  first.  An  ideal 
site  should  be  so  situated  that  the  ore  from  the  mine  may  be 
dumped  into  the  mill  storage  bin  in  the  least  possible  time,  without 
being  handled  by  any  other  than  mechanical  means  and  by  as  little 
machinery  as  possible,  and  requiring  little  if  any  power.  At  the 
same  time  it  must  be  kept  in  mind  that  waste  must  also  be  drawn 
from  the  mine  and  carried  to  a  suitable  dump,  if  possible  by 
mechanical  means  and  with  little,  if  any,  expenditure  of  power. 
An  ideal  situation  in  this  respect  would  be  one  in  which  the  ore 
from  the  tunnel  or  shaft  could  be  dumped  automatically  from 
the  car  or  skip  into  the  mill  bin,  and  the  waste  into  a  chute  or  down 
an  incline  to  a  canyon  or  gully  being  both  steep  enough  to  carry  it 
away  by  gravity  and  sufficiently  large  to  provide  storage  for  all  the 
waste  produced  during  the  life  of  the  mine.  Following  this,  the 
site  should  be  situated  on  a  hill  side  of  sufficient  incline  to  permit 
the  ore  and  pulp  to  flow  by  gravity  through  each  successive  stage 
in  the  treatment,  and  thus  avoid  the  use  of  pumps  or  elevators 
for  handling  the  pulp  during  the  course  of  treatment. 

The  ground  should  be  solid  rock  in  order  to  provide  a  suitable 
foundation  for  the  heavy  machinery,  so  that  it  may  run  with  a 
minimum  of  vibration,  thereby  reducing  breakages  and  permitting 
the  best  possible  performance  to  be  obtained  from  the  concentra- 
tors, which,  on  account  of  the  peculiar  nature  of  their  own  vibratory 
movement,  are  seriously  affected  by  insecure  foundations.  The  last 
requirement  is  that  means  should  be  provided  for  the  disposal  of 
the  tailing.  The  storage  ground  or  runway  should  have  a  capacity 
equal  to  the  life  of  the  mine,  and  should  have  sufficient  incline  to 
allow  the  tailing  to  flow  away  from  the  mill  by  gravity. 


COST   OF    CONSTRUCTING   STAMP-MILLS  211 

The  constructor  or  builder,  however,  looks  upon  the  question  in 
an  entirely  different  light.  The  only  features  of  interest  to  him  are 
those  influencing  the  cost  of  construction.  He  would  like  a  site 
where  the  ground  is  comparatively  soft,  in  order  to  have  a  low 
cost  of  grading,  and  yet  hard  enough  so  that  the  cost  of  retaining 
walls  and  foundations  could  be  kept  down.  A  flat  spot,  as  close  to 
tke  millsite  as  possible,  and  large  enough  for  a  framing  yard  and 
for  the  storage  and  shaping  of  timber  and  lumber,  is  most  desirable. 
Proximity  to  the  wagon  road  over  which  the  freight  and  material 
is  transported  is  also  desirable,  as  moving  heavy  material  and 
machinery  by  hand  is  costly  and  is  to  be  avoided  as  much  as  possi- 
ble. The  site  should  not  be  too  steep  so  that  the  cost  of  grading 
becomes  unnecessarily  high,  neither  should  it  be  too  flat  or  an  ex- 
pensive and  heavy  timber  supporting  structure  may  have  to  be 
built.  A  millsite  on  an  angle  of  30°,  with  a  leeway  of  5°  either 
way,  will  be  found  to  be  nearly  ideal  for  mills  that  include  crushers, 
stamps,  and  concentrators.  In  view  of  these  facts  the  folly  of  ob- 
taining a  'stock'  plan  from  a  manufacturer  and  cutting  up  a  mill- 
site  to  suit  it  will  be  apparent  at  once.  There  are  very  few  men 
buying  a  small  mill  of  10  stamps  who  have  the  remotest  idea  of 
the  influence  of  the  topography  of  their  millsite,  but  take  a  set  of 
stock  plans  from  the  manufacturer  of  the  machinery,  and,  when 
ready  to  commence  construction  try  to  find  a  site  to  fit  the  plan  in- 
stead of  making  plans  to  fit  the  site.  When  the  mine  owner  is 
ready  to  proceed  with  the  construction  of  a  mill,  a  surveyor  should 
be  put  to  work  making  both  contours  and  a  profile  of  the  site  of 
the  proposed  mill.  With  this  information  in  hand  a  manufacturer 
or  engineer  can  design  the  mill  to  suit  the  site. 

Cost  of  Constructing  Stamp-Mills. — Estimating  on  the  cost 
of  stamp-mill  construction  is  not  an  exact  science.  No  engineer  or 
contractor  can  see  far  enough  into  the  future  to  know  beforehand 
what  unusual  or  unexpected  conditions  will  arise  during  the 
progress  of  construction,  any  of  which  will  influence  the  cost  of 
the  work.  The  following  has  been  written  primarily  for  those  who 
contemplate  the  erection  of  small  mills  up  to  20  stamps  in  size. 
It  gives  the  average  cost  of  the  various  classes  of  work,  and  the 
various  elements  entering  into  construction  costs  are  briefly  pointed 
out,  with  the  object  in  view  of  furnishing  a  basis  by  which  a  man 
familiar  with  the  ground  on  which  the  mill  is  to  be  erected  may 
prepare  an  intelligent  estimate. 

There  is  an  idea  prevalent  among  mining  men  in  general  that 
stamp-mills  can  be  built  complete  and  turned  over  in  running  order 


212  COST   OF    CONSTRUCTING   STAMP-MILLS 

for  $1000  per  stamp.  This  estimate  may  be  correct  in  possibly  one 
case  in  a  hundred,  and  as  no  two  sets  of  conditions  governing  the 
cost  of  mill  construction  are  exactly  alike,  the  use  of  this  formula — 
if  it  may  be  so  called — can  only  result  in  disappointment.  The 
figures  here  given  are  based  upon  California  conditions  of  labor  and 
climate,  the  rate  of  wages  being  as  follows  per  8-hour  shift :  mill- 
wrights, $5 ;  carpenters,  $4 ;  helpers,  $3 ;  masons,  $5 ;  machinists,  $4. 
The  elements  entering  into  the  cost  of  stamp-mill  construction  will 
each  be  treated  separately,  and  will  all  be  found  in  the  following 
summary.  This  affords  a  good  form  for  preparing  estimates,  and 
will  be  of  aid  in  itemizing  the  factors  which  make  up  the  total  cost : 

MATERIAL 

Machinery  f.o.b.  factory. 

Lumber  for  mill  building  f.o.b.  shipping  point. 

Timber  for  ore-bin  and  battery-frame  f.o.b.  shipping  point. 

Shingles  or  shakes  for  roof. 

Galvanized  corrugated  iron  for  sides  and  roof. 

Doors. 

Windows. 

Building  hardware. 

Nails. 

Cement. 

Sard. 

Broken  rock. 

Building  bolts  and  washers. 

Red  brick. 

Fire  brick. 

Fire  clay. 

Lime. 

Tools  for  construction. 

Freight  charges  on  all  the  above  from  shipping  point  to 

railroad  station  nearest  mine. 
Hauling  charges  on  all  the  above  from  railroad  station  to 

millsite. 

LABOR 

Framing  and  erecting  building. 

Putting  on  siding;  shingle  roof;  shake  roof. 

Iron  siding  and  roof. 

Setting  doors  and  windows. 

Erecting  machinery. 

Handling  building  material  and  machinery  on  the  ground. 


COST   OP    MACHINERY  213 

Framing  and  erecting  battery-frame ;  ore-bin. 

Grading  and  excavating. 

Masonry  retaining  walls. 

Concrete  retaining  walls. 

AVood  mortar-block. 

Concrete  mortar-block. 

Concrete  foundations. 

Brick  setting  for  steam-boiler. 

Superintendence. 

Timekeeper  and  office  work. 

Allowance   for  unforseen   contingencies. 

MACHINERY,  COST  AT  FACTORY.— This  information  is  the 
easiest  of  all  to  obtain,  and  an  inquiry  sent  to  any  reputable  machinery 
manufacturer  will  meet  with  a  prompt  response.  Modern  trade  cata- 
logues are  so  carefully  prepared  and  enter  into  so  much  detail  that 
they  are  practically  text-books  on  machinery  construction  and  design. 
Most  machinery  houses  maintain  a  competent  engineering  depart- 
ment, which  will  co-operate  with  prospective  customers  and  assist 
them  in  making  proper  selection  of  the  machinery  best  suited  for 
treating  their  ores.  Much  time  will  be  saved  if  prospective  buyers 
will  give  the  manufacturer  a  definite  idea  of  conditions  to  be  met 
in  order  that  an  intelligent  estimate  may  thus  be  prepared.  In 
sending  an  inquiry  to  a  manufacturer  for  prices  of  mill  equipment 
it  is  necessary  that  he  should  be  informed  as  to  (a)  character  of  the 
ore;  (&)  process  that  is  to  be  used;  (c)  number  of  tons  per  day  of 
24  hours  that  it  is  desired  to  treat ;  (d)  fineness  to  which  it  is  desired 
to  crush ;  (<?)  kind  of  power  to  be  used ;  (/)  probability  of  increasing 
the  capacity  and  size  of  the  plant  in  the  future. 

If  conditions  require  gasoline-engines  for  power,  the  altitude 
above  sea-level  at  the  millsite  must  be  stated,  as  internal-combustion 
engines  lose  about  3%  efficiency  for  each  1000  ft.  rise  above  sea- 
level.  If  steam-power  is  to  be  used,  the  kind  of  fuel  should  be 
stated. 

If  electricity  is  to  be  used,  the  voltage  must  be  stated  if  current  is 
continuous ;  phase,  voltage,  and  frequency  must  be  stated  if  the  cur- 
rent is  alternating.  If  transformers  are  required,  primary  voltage 
and  phase  must  be  stated. 

If  water-power  is  to  be  used,  the  manufacturer  must  know  the 
quantity  of  water  available  in  cubic  feet  or  gallons  per  minute  or 
miner's  inches,  and  the  head  in  feet  or  vertical  distance  between 
point  of  intake  and  point  of  outlet.  If  pipe-line  is  already  in  place, 


214  COST   OF    CONSTRUCTING   STAMP-MILLS 

length  and  diameter  must  be  stated;  and  if  not  already  in  place, 
the  length  only  will  suffice. 

ERECTION  OF  MACHINERY.— This  is  an  item  which  may  cost 
from  $30  per  ton  upward,  depending  upon  the  skill,  ingenuity,  and 
experience  of  the  man  in  charge  of  construction.  After  all  orders  for 
machinery,  building  material,  and  supplies  have  been  placed,  instruc- 
tions should  be  sent  to  the  various  concerns  furnishing  material,  for 
the  purpose  of  arranging  a  systematic  schedule  of  shipping  dates,  so 
as  to  have  the  machinery  and  other  material  arrive  on  the  ground  as 
nearly  as  possible  in  the  sequence  in  which  it  is  required.  There  is  sel- 
dom any  gain  in  attempting  to  rush  all  shipments  indiscriminately,  as 
the  confusion  and  chaos  on  the  ground  will  result  in  more  lost  time 
and  delay  than  is  gained  by  quick  though  unsystematic  shipments.  If 
foundations  are  ready  for  the  heavy  machinery,  the  latter  can  be 
lifted  direct  from  wagons  and  set  in  its  proper  place  in  the  mill; 
otherwise  it  may  have  to  be  handled  two  or  three  times,  and  each 
time  it  is  handled  it  costs  money. 

Bolts,  washers,  and  small  fittings  when  unpacked  from  shipping 
cases  should  be  systematically  arranged  according  to  size ;  this  can 
be  attended  to  by  a  boy  or  laborer  when  not  engaged  on  more  urgent 
work.  Often  a  $5-per-day  man  will  spend  an  hour  looking  through 
a  pile  of  small  parts  for  a  bolt,  which  should  have  had  its  place  and 
been  in  it.  Manufacturers  generally  send  out  a  detailed  statement 
with  each  shipment  showing  the  contents  of  each  package  and  case, 
so  there  is  no  excuse  for  waiting  until  a  job  is  nearly  ready  to  turn 
over  and  then  find  that  the  work  must  be  hung  up  and  a  crew  of 
men  stand  around  idle,  waiting  for  some  small  detail  or  missing  part 
which  may  have  been  overlooked  at  the  factory  or  lost  by  careless 
unpacking  of  material.  Small  parts  and  fittings  liable  to  be  lost  or 
damaged  by  exposure  to  the  weather  should  be  housed.  Even  the 
crudest  kind  of  a  shed  will  save  its  cost  many  times  over  during 
construction  of  the  plant.  Building  material,  lumber,  etc.,  should 
receive  the  same  care  and  systematic  handling  as  machinery  and 
supplies.  It  is  surprising  how  much  time  and  money  can  be  saved 
by  a  little  foresight  in  this  direction.  A  suitable  framing  yard 
should  be  prepared,  as  near  the  millsite  as  possible,  in  which  all 
lumber  can  be  systematically -stacked  on  arrival  according  to  width, 
thickness,  and  length,  and  where  all  framing  can  be  done.  Carrying 
lumber,  heavy  timbers,  etc.,  back  and  forth  by  manual  labor  and 
trying  to  make  a  good  job  of  framing  when  working  on  a  side-hill 
are  not  compatible  with  low  costs.  "When  a  man  has  spent  much 
of  his  time  and  money  in  developing  a  prospect,  and  then  has  spent 


COST   DUE   TO   LUMBER  215 

more  time  and  hard  work  in  financing  his  company,  it  can  be  readily 
understood  why  he  is  impatient  to  get  started,  but  he  should  stop 
to  consider  that  it  nearly  always  costs  as  much  money  to  try  to  force 
work  ahead  at  a  pace  faster  than  circumstances  will  permit,  as  it 
would  to  go  to  the  other  extreme  and  delay  matters. 

FREIGHT  AND  HANDLING.— These  two  items  are  governed  en- 
tirely by  local  conditions,  and  no  general  information  on  this  subject 
can  be  given ;  therefore,  calculations  must  necessarily  be  made  in  each 
case  according  to  circumstances. 

LUMBER  FOR  MILL  BUILDING.— The  first  cost  of  lumber  is 
governed  by  local  conditions  and  by  the  prevailing  market  price  exist- 
ing at  the  time  the  order  is  placed.  The  labor  cost  is  also  a  variable 
factor,  depending  upon  local  conditions  and  the  individuality  of 
the  workman  himself,  but  the  following  rates  will  give  a  fairly  close 
average  approximation: 

Framing  and  erecting  mill  buildings  up  to  30  ft.  in  height,  $25 
per  M  board-feet. 

Framing  and  erecting  mill  buildings  30  ft.  in  height  and  upward, 
including  setting  roof-trusses,  $35  per  M  board-feet. 

Putting  on  1-in.  rough  siding,  battened,  laying  wood  floor,  etc., 
$20  per  M  board-feet. 

It  has  been  found  by  actual  experience  that  a  workman  can  work 
about  half  as  fast  at  a  height  of  30  ft.  or  over  as  he  can  when  be- 
low that  point,  and  for  this  reason  roof-trusses  should  always  be 
framed  and  put  together  complete  on  the  ground,  then  hoisted  into 
place  and  fastened,  rather  than  be  put  together  in  position  by 
piece-meal. 

Underestimating  the  quantity  of  lumber  required  is  a  mistake 
frequently  made.  The  principal  cause  of  this  is  that  the  inexper- 
ienced estimator  figures  merely  the  superficial  area  to  be  covered 
and  the  net  lengths  of  the  timbers  for  the  building  framework, 
whereas  lumber  is  always  cut  in  mill  standard  lengths,  breadths,  and 
thicknesses,  and  will  have  to  be  ordered  accordingly.  A  wise  pre- 
caution is  to  obtain  such  a  list  from  the  lumber  dealer  before  com- 
mencing to  figure  the  lumber  bill.  The  dealer,  however,  does  not 
always  carry  in  stock  all  of  the  sizes  listed.  Inform  yourself  as  to 
exactly  what  sizes  are  carried  and  make  your  calculations  accord- 
ingly. If  the  concentrator  room,  for  instance,  is  shown  10  ft.  6  in. 
high  on  the  plans,  every  post,  piece  of  siding,  and  batten  will  have 
to  be  ordered  12  ft.  long  as  there  is  no  intermediate  length  made 
between  10  and  12  ft.  Any  normal  surplus  of  lumber  remaining 
after  completion  of  the  mill  will  soon  be  used  for  other  purposes. 


216  COST    OF    CONSTRUCTING    STAMP-MILLS 

Such  items  as  launders  and  lumber  for  concrete  forms  are  also 
frequently  omitted  in  estimates,  and  yet  require  an  appreciable 
quantity  of  lumber.  Another  item  that  is  a  frequent  source  of 
underestimation  is  the  cost  of  freight  and  hauling  lumber.  Dry 
pine  lumber  weighs  about  3*4  lb.  per  board-foot.  It  is  stored  out 
in  the  open,  exposed  to  all  kinds  of  weather.  It  has  a  wonderful 
capacity  for  absorbing  moisture,  and  while  dry  lumber  may  and 
does  weigh  about  3*4  Ib.  per  board-foot,  wet  lumber  often  weighs 
50%  over  this  amount.  A  simple  expedient  is  to  ask  the  lumber 
dealer  to  quote,  delivered  at  destination.  This  course  will  protect 
you,  and  perhaps  save  a  shock  when  you  come  to  compare  actual 
cost  with  your  estimate. 

The  table  on  the  opposite  page  will  be  of  assistance  in  figuring 
lumber  bills  and  the  quantity  required. 

ORE -BIN  AND  BATTERY-FRAME.— The  same  remarks  as  re- 
gards first  cost  of  material  apply  in  this  case  as  in  that  for  lumber 
for  the  mill  building  proper.  Dressed  timber  need  not  necessarily  be 
used,  although  many  builders  prefer  it  on  account  of  appearances. 
Occasionally  builders  prefer  to  have  the  timber  furnished  already 
cut  and  framed  where  machine  tools  are  available,  on  the  ground 
of  economy,  but  it  is  questionable  whether  this  course  pays  in  the 
long  run,  since  sufficient  stock  must  always  be  left  to  allow  for  trim- 
ming when  lining  up  the  frame,  camshaft  bearings,  and  guide  girts, 
which  work  cannot  be  done  until  the  machinery  is  actually  in  course 
of  erection.  The  cost  of  framing  and  erecting  a  battery-frame  and 
ore-bin,  including  planking,  is  about  $35  per  M  board-feet. 

SHINGLES  FOR  ROOFING.— The  following  schedule  will  apply 
to  ordinary  mill  roofs,  250  shingles  being  1  bundle :  Using  pine  shingles 
with  4  in.  exposed  to  the  weather,  1000  shingles  per  square  will  be 
required,  weighing  approximately  245  Ib.  If  6  in.  be  exposed  to  the 
weather,  670  shingles  per  square  will  be  required,  weighing  approxi- 
mately 165  Ib.  Sheathing  should  be  4  in.  wide  and  spaced  4  in. 
apart.  A  square  equals  10  by  10  ft.,  or  100  sq.  ft.  Labor  cost  per 
square  is  approximately  $1.50. 

SHAKES  FOR  ROOFING.— There  is  quite  a  variation  in  the  size 
of  shakes  as  furnished  by  the  different  mills,  but  the  ordinary  shake 
may  be  considered  to  be  6  in.  wide  and  from  32  to  36  in.  long.  With 
10  in.  exposed  to  the  weather,  250  shakes  per  square  will  be  required. 
Sheathing  should  be  6  in.  wide  and  spaced  5  in.  apart.  Labor  cost 
per  square  is  approximately  $1.25. 

DOORS  AND  WINDOWS.— The  ordinary  12-light,  10  by  12-in., 
single  windows  are  ordinarily  used,  the  price  varying  according  to 


COST   OF    IRON    SIDING 


217 


local  conditions.  Labor  cost  of  setting  windows  is  approximately  $1.50 
each.  Plain  doors,  2  ft.  8  in.  by  6  ft.  8%  in.,  will  vary  in  cost  accord- 
ing to  local  conditions.  Labor  cost  of  setting  is  approximately  $1.50 
each.  Ordinary  plain  hardware  used  on  windows  and  doors  should 
not  cost  to  exceed  $2.50  per  door  or  window. 

NUMBER  OF  FEET,  BOARD  MEASURE,  IN  LUMBER  OF  VARIOUS  SIZES 


Size  in  inches. 
by    2  .. 

UJiJrr:: 

10. 
1% 
2% 
3*4 

12. 
2 
3 
4 

14. 
2% 
3% 
4% 

16. 
2% 
4 

5% 

18. 
3 
4% 
6 

20. 

P 

6% 

1 
7% 

M 

4 
• 
8 

by    5  

4% 

6 
6 

5% 
7 

6% 

8 

P 

8k 
10 

«% 

by    7  

SiS  ::::::::::: 

by  12  

5% 
6% 

8% 

10 

11% 

7 
8 
10 
12 

SVe 
9>/3 
11% 
14 
16% 

«% 

10% 
13% 
16  • 
18% 

10% 
12 
15 
18 
21 

11% 
jjg 
23% 

12% 
14% 
18% 
22 
25% 

by  16  
by  18  

.:::::::::  5* 

16% 

18 

18% 
21 

21% 
24 
26% 

24 

27 

26% 
30 

s* 

/i  by    4  
y*  by    6  
Vt  by    8  
/4  by  10  
Vi  by  12  

4i/6 
6% 
8% 
!<)•/„ 
12% 

5 

7% 

10 
12% 
15 

5'/« 
8% 
11% 
"'/„ 

17% 

6% 
10 
13% 
16% 
20 

7% 

uy* 

15 
18% 
22% 

8% 
12% 
16% 
20V. 
25 

9% 
13% 
18% 
22-/U 

27% 

A  by    4  
%  by    6  
/Zby    8  
%  by  10  

7y2 

12% 

9 
12 
15 

10'/2 
14 
17% 

12 
16 
20 

13% 
18 
22% 

15 

25 
30 

16% 
22 
27% 

by    4  
by    6  
by    8  
V  10  

6% 
10 

13% 

16% 

8 
12 
16 
20 

91/3 
14 
18% 

2sy3 

10% 
16 
21% 
26% 

12 
18 
24 
30 

%* 
26% 
33% 

14% 

22 
29% 
36% 

by  14  
by  16  

23% 

26% 

28 
32 

32% 
37% 

37% 

42% 

42 
48 

46% 
53% 

51% 

58% 

y2  by  14  

29ys 

35 

4oy« 

46% 

52% 

58% 
66% 

64% 
73% 

by    6  
by    8  
by  10  
by  12  
by  14  
by  16  
by    4  

15 
20 
25 
30 
35 
40 

'-    %* 

18 
24 
30 
36 
42 
48 
16 

21 

35 
42 
49 
56 
18% 

24 
32 
40 
48 
56 
04 
21% 

27 
36 
45 
54 

72 
24 

30 
40 
50 
60 
70 
80 
26% 
40 

44 
55 
66 
77 
88 
29% 
44 

by    8  

26% 

32 

37% 

42% 

48 

53% 
66% 

58% 
73% 

V12  
by  14  
by    6  
by    8  

40 
46% 
30 
40 

48 
56 
36 
48 

56 
65% 
42 
56 

64 
74% 
48 
64 

72 
84 
54 
72 

80 
93% 
60 
80 

88 
102% 
66 
83 

I't: 

by  12  
by  14  
by  16  
by    8  
by  10 

60 
70 
80 
53% 

72 
84 
96 
64 

84 
98 
112 
74% 

96 
112 
128 
85% 

108 
126 
144 
96 
120 

120 
140 
160 
108% 
133% 

132 
154 
176 
117% 
146% 

114 

MS 
1H2 
12S 
W 

by  12  
by  14  
by  10  
10      by  12  
0      by  14  
10      by  16  
12      by  12  
12      by  14  
12      iy!6...,  
14      by  14  
14      by  16     

80 
931/3 
83% 
100 
:.  116% 
133% 
120 
140 
160 

'.'.'.'.'.'.'.'.'.'.  186%. 

96 
112 
100 
120 
140 
160 
144 
168 
192 
196 
224 

112 

130% 

140 

i6sy3 

186% 
168 
196 
224 
228% 
26iy3 

149% 
133% 
160 
186% 
213% 
192' 
224 
256 
261% 
298% 

144 
168 
150 
180 
210 
240 
216 
252 
288 
294 
336 

160 
186% 
166% 
200 

266% 
240 
280 
320 
326% 
373% 

176 

205% 

22o' 
256% 
2931/3 
264 
303 
352 
3591/3 
410% 

l!i- 

KM 

-ii' 
Ml 

•_'.' 

a 

w 

:;:: 

n 

H 
411 

IRON  BUILDING. — In  many  localities,  particularly  the  desert 
country,  where  lumber  is  scarce  and  the  cost  is  correspondingly  high, 
galvanized  corrugated  iron,  and  sometimes  flat  painted  iron  sheets, 
are  used  for  the  sides  and  roofs  of  buildings.  The  price  of  this 
material  varies  with  market  conditions  and  locality.  The  following 


218 


COST   OP    CONSTRUCTING   STAMP-MILLS 


table  will  be  of  assistance  in  making  calculations  as  to  the  quantity 
required : 

NUMBER  OF  CORRUGATED  SHEETS  PER  SQUARE 


rugation 
at,  30  i 
ter  corr 
7  in.  N 
width,  2 


S  fc 

£0  O 


Length  of 
sheet, 
inches. 

f^&SS 

jpElU 

55PSSS 

60    

8.572 

8.888 

9.231 

72    

7.143 

7.407 

7.692 

84    

6.122 

6.349 

6.593 

96    

5.357 

5.555 

5.769 

108    

4.762 

4.938 

5.128 

120    

4  286 

4.444 

4.616 

If  material  is  painted,  add  20  Ib.  per  square  to  allow  for  paint. 
No.  26  is  the  gauge  usually  used  for  both  roof  and  sides,  although 
No.  28  sides  are  sometimes  deemed  heavy  enough.  The  labor  cost 
for  fastening  roof  and  sides  is  approximately  $1.25  per  square. 

WEIGHT  OF  CORRUGATED  SHEETS  PER  SQUARE 

,  --  Black  -  ^         ,  -  Galvanized  -  , 


3-in.     2%-in.     1*4  -in.        3-in.     2%  in. 


in. 


Gauge. 


cor. 

166 

152 

138 

125 

111 

97 

83 

76 

69 


cor. 

167 

153 

139 

125 

111 

97 

83 

76 

69 


cor. 
170 
156 

142 
127 
113 

99 
85 
78 
71 


cor. 
183 
170 
156 
142 
128 
114 
100 
93 


cor. 
184 
170 
156 
142 
128 
115 
101 
94 
87 


cor. 
187 
173 
159 
145 
131 
117 
103 


NAILS. — The  quantity  of  nails  of  each  size  required  for  each  class 
of  work  may  be  fairly  accurately  calculated,  provided  that  there  is 
no  excessive  waste,  and  the  following  tabulation  will  be  found  to  be 
close  enough  for  all  ordinary  purposes: 

Use: 

For  each:  Pounds.     Size. 

1000  shingles 4  4d 

31/2         3d 

1000  laths  6  3d 

1000  ft.  clapboarding 18  6d  box  nails 


COST   OF   NAILS 


219 


For  each: 
1000  ft   siding     

Use: 
Pounds.     Size. 
20             8d 

10  ft  partition  shedding 

25           lOd 
1           K)d 

1000  ft   1  by  3  flooring 

45           lOd 

1000  ft  1  by  2  flooring 

65           lOd 

1000  ft   pine  finish     

30             8d 

250  shakes  .  . 

21/0         5d 

STANDARD  STEEL  WIRE  NAILS 


Size. 

Length. 

2 

1 

3 

4  

1% 

5  

1% 

6  

2 

7  

....'  2% 

8  

21/2 

10 

3 

12  

3% 

16 

3V» 

20  

4 

30  

4V2 

40  

5 

50  

5% 

60   

6 

(Note.—  100  Ib.  equals  1  keg.) 

SHINGLE  NAILS 

Size. 

Length. 

3  

114 

4  

1% 

5  

1% 

6  

2 

7  

2% 

8  

21/2 

9  

2% 

10  

3 

Approx.  No 

Gauge  No. 

per  Ib. 

15 

876 

14 

568 

12% 

316 

12  y2 

271 

11% 

181 

11  % 

161 

10% 

106 

10% 

96 

9 

69 

9 

63 

8 

49 

6 

31 

5 

24 

4 

18 

3 

14 

2 

11 

Gauge  No. 
13 
12 
12 
12 
11 
11 
11 
10 


Approx.  No. 

per  Ib. 

429 

274 

235 

204 

139 

125 

114 

83 


A  special  barbed  galvanized  nail  is  used  for  attaching  corrugated 
or  painted  sheets  to  wood-frame  buildings,  and  is  driven  first  through 
a  lead  washer,  then  through  the  iron  into  the  wood  frame.  In  this 
work  11/2  Ib.  of  2-in.  No.  9  galvanized  barbed  nails  are  sufficient  for 
one  square ;  325  lead  washers,  weighing  1  Ib.,  are  sufficient  for  about 
two  squares. 

BUILDING  BOLTS.— As  this  item  is  one  that  is  subject  to  great 


220  COST   OF    CONSTRUCTING   STAMP-MILLS 

variation,  depending  upon  the  ideas  of  individual  mill  designers,  it 
is  difficult  to  give  information  that  will  be  even  approximately 
correct  without  publishing  mill  drawings  also.  In  the  treatment  of 
free-milling^  gold  ores  by  amalgamation  only,  the  building  bolts  for 
a  5-stamp  mill  will  weigh  approximately  500  Ib. ;  a  10-stamp  mill, 
1000  Ib.;  a  20-stamp  mill,  2000  Ib.  It  is  quite  possible  to  design  an 
excellent  building  in  which  building  bolts  are  almost  entirely  omit- 
ted, and  it  should  be  understood  that  the  above  information  should 
be  used  for  what  it  is  worth  and  no  more.  It  is  a  comparatively 
simple  task  to  calculate  the  number  and  cost  of  bolts  required  when 
drawings  are  made  and  submitted  by  the  designer. 

GRADING  AND  EXCAVATING.— This  is  the  most  difficult  of  all 
to  treat  in  generalities,  as  the  following  factors  are  commonly  all  vital 
as  far  as  costs  are  concerned  and  vary  widely  in  each  locality :  (a)  cost 
of  labor;  (&)  character  of  the  ground;  (c)  cost  of  powder,  fuse,  and 
caps  on  the  ground ;  (d)  whether  machine  drills  or  hand  drills  are 
used.  The  average  millsite  has  an  overburden  of  earth  of  varying 
thickness  which  can  ordinarily  be  moved  by  hand-picking  and 
shoveling,  with  possibly  a  few  shots  to  loosen  it  thoroughly.  On 
ground  of  this  nature  one  man  can  remove  about  10  yd.  in  an  8-hour 
day,  but  if  it  must  be  handled  in  wheelbarrows  for  any  considerable 
distance,  the  cost  will  probably  equal  $1.25  to  $1.50  per  yard.  On 
solid  rock,  however,  where  the  rock  is  hard  and  tough  and  does  not 
shatter  readily,  and  where  hand-drilling  is  necessary,  one  yard  for 
two  men  per  day  will  be  as  much  as  could  be  expected ;  especially 
if  the  rock  must  be  bulldozed  after  breaking  in  order  to  get  it  down 
to  pieces  small  enough  to  be  shoveled  by  hand  and  hauled  away  in 
wheelbarrows.  These  two  cases  illustrate  the  extremes  in  the  cost 
of  grading,  and  costs  covering  average  conditions  will  be  somewhere 
between  these  two.  A  mill  grade  of  large  size  has  been  made  as 
cheaply  as  $1.50  per  yard  for  the  shooting  ground  where  all  con- 
ditions were  exceptionally  favorable. 

POWDER  REQUIRED.— In  one  specific  case,  shooting  fairly  hard 
rock,  3420  yd.  required  750  Ib.  of  40%  giant,  and  800  Ib.  of  60%  giant 
for  bulldozing.  The  fuse  cost  about  2c.  per  yard  and  caps  le.  per 
yard.  When  the  mine-owner  has  carried  his  underground  development 
far  enough  along  to  warrant  fully  his  considering  the  purchase  and 
construction  of  a  mill,  he  will  have  had  sufficient  experience  in 
breaking  his  own  ground  to  calculate  the  cost  of  his  mill  grading 
accurately. 

RETAINING  WALLS  AND  FOUNDATIONS.— Retaining  walls 
are  not  required  unless  the  ground  is  of  such  a  character  that  it  will 


COST   OF    CONCRETE   WORK  221 

not  stand  without  them.  They  may  be  built  either  of  masonry  or  con- 
crete, depending  entirely  upon  the  material  available  on  the  ground 
That  required  for  concrete  walls  is  rock  (hard,  sharply  broken,  and 
absolutely  free  from  dirt,  clay,  or  other  foreign  substances),  clean 
sharp  sand,  first  quality  portland  cement,  and  water.  Another  com- 
bination sometimes  used  is  broken  rock,  sand,  gravel,  cement,  and 
water,  and  while  this  latter  will  answer  for  retaining  walls,  it  is  not 
as  satisfactory  for  machinery  foundations  or  mortar-blocks  as  the 
first  combination  given. 

Walls  are  calculated  by  the  perch,  a  perch  being  IG1/^  by  1M>  by 
1  ft.  and  containing  24%  cu.  ft.  To  make  one  perch,  use  2500  Ib.  of 
broken  rock,  1250  Ib.  of  sand,  and  625  Ib.  of  cement.  The  propor- 
tions ordinarily  used  are  1:2:4  for  cement,  sand,  and  broken  rock 
and  1:2:4:8  for  cement,  sand,  gravel,  and  broken  rock.  Lime  is 
sometimes  used  instead  of  cement  on  account  of  its  cheapness,  but 
it  does  not  give  nearly  as  great  strength  or  permanency  as  cement. 

The  following  cost  of  retaining  walls  for  a  40-stamp  mill  built  in 
Arizona  will  give  an  idea  of  the  cost  of  this  type  of  construction 

Perch. 

Concentrator-room  wall  contained 135 

Battery-room  wall  contained 371 

Total 506 

Cost  of  the  above  was  made  up  as  follows: 

68%  bbl.  of  lime  cost,  delivered $157 

63  cu.  yd.  of  sand  cost,  delivered   50 

Labor:  mason  59  days,  helper  161  days,  cost 668 

Total $875 

Cost  per  perch,  $1.72. 
(Note. — Broken  rock  was  available  on  the  ground  without  charge.) 

Concrete  foundations  ordinarily  cost  from  $6.50  to  $7.50  per  cubic 
yard  finished,  when  cement  costs  $3.50  per  barrel  delivered ;  labor, 
$2.25  per  yard;  and  boxes,  $0.40  per  yard.  A  barrel  of  cement 
weighs  400  Ib.,  and  is  equivalent  to  4  sacks  containing  1  cu.  ft.  each. 

A  man  inexperienced  in  concrete  work  should  not  attempt  to 
select  rock,  sand,  or  gravel  for  this  purpose,  but  should  obtain  the 
advice  of  .some  one  familiar  with  the  requirements  of  this  work. 
Otherwise  failure  is  altogether  likely  to  follow.  Not  all  rock  is 
suitable,  by  any  means,  and  care  in  selecting  raw  material  will  be 
repaid  in  the  superior  quality  of  the  finished  product. 

CONCRETE  FL  00  US  .—Concrete  floors  are  generally  made  4  in. 
thick  and  require  no  forms  or  boxes,  but  are  made  from  the  regular 


222 


COST    OP    CONSTRUCTING   STAMP-MILLS 


concrete  mixtures  already  mentioned,  with  a  thin  top-dressing  of  a 
thick  cement  grouting  to  give  a  smooth  finish.  The  following  case 
will  give  a  fair  general  average  idea  as  to  what  may  be  expected  for 
cost  of  concrete  floors : 

Floor  contained  6680  sq.  ft,  4  in.  thick.    To  make  this  floor  required: 

76  bbl.  of  cement  costing  delivered $406 

Labor:  mason  40  days,  helper  80  days,  costing... 375 


Total 

Average  cost  per  100  sq.  ft.,  $12. 

(Note. — Broken  rock  and  sand  were  available  on  the  ground  without 
charge.) 

STEAM-BOILER  SETTING.— Every  boiler  manufacturer  has  his 
own  designs  for  boiler  setting  and  publishes  a  schedule  for  the  num- 
ber of  brick  and  fire-brick  required,  but  the  following  table  will 
answer  for  approximate  estimates  to  cover  the  setting  of  single 
tubular  boilers  with  half  fronts : 

No.  fire- 
brick. 
550 
550 
650 
720 
770 
880 
940 
1020 
1140 
1140 
1270 
1270 
1540 
1900 

In  making  comparisons  between  boilers  designed  for  a  brick 
setting  as  compared  with  the  locomotive  fire-box  and  the  internally 
fired  types,  the  latter  should  always  be  considered  as  requiring  a 
covering  of  asbestos  2  or  3  in.  thick  in  order  to  reduce  the  radiation 
losses  and  keep  the  fuel  consumption  down.  Common  red  brick 
weigh  5  Ib.  each,  and  standard  fire-brick  7  Ib.  each.  A  4y2-in.  wall 
equals  7  brick  per  square  foot  of  surface ;  a  9-in.  wall  equals  14 ;  a 
13-in.,  20;  18-in.,  26V2 ;  21-in.,  33;  27-in.,  39V2  brick.  The  weight  of 
walls  is  112  Ib.  per  cubic  foot  in  red-brick  work  and  150  Ib.  in  fire-brick 
work.  A  cubic  foot  of  red-brick  work  equals  17.9  in.  straight  brick, 
and  1  cu.  ft.  of  silica-brick  work  weighs  130  Ib.  In  making  estimates 
on  red-brick  work,  consider  that  9  cu.  ft.  of  sand  and  3  bushels  of 


Diameter, 

Length, 

Horse- 

No. red 

inches. 

feet. 

power. 

brick. 

30   

7 

10 

6,000 

30    

8 

12 

6,200 

36    

8 

15 

6,700 

36    

10 

20 

7,050 

42    

10 

25 

8,700 

44    

10 

30 

8,800 

44    

12 

35 

9,300 

44    

14 

40 

10,800 

48    

14 

45 

12,900 

48    

15 

50 

13,700 

54    

15 

60 

14,200 

54    

16 

70 

15,000 

60    

16 

80 

21,500 

60    

16 

100 

25,000 

COST    OF    MORTAR-BLOCKS  223 

lime  will  lay  1000  brick,  and  that  250  to  350  Ib.  of  fire-clay  or  silica 
cement  will  lay  1000  fire-brick.  A  bricklayer  will  ordinarily  lay 
from  1200  to  1500  brick  per  day  of  8  hours. 

CONCRETE  MORTAR-BLOCKS.— As  there  are  many  different 
ideas  as  to  method  of  construction  and  proportions  of  material  to  be 
used,  there  will  be  given  three  specific  instances  of  blocks  which  have 
been  built  and  in  use  for  a  sufficient  number  of  years  to  determine 
their  practicability.  They  represent  what  may  be  considered  as  typ- 
ical cases,  and  will  give  fair  average  conditions  between  the  cheaper 
and  simpler  forms  of  blocks  and  the  more  elaborate  and  expensive. 

The  first  case  to  be  given  covers  the  blocks  used  for  a  40-stamp 
mill,  which  after  ten  years  continuous  operation  have  proved  per- 
fectly satisfactory.  The  stamps  weighed  1000  Ib.  each  when  new, 
and  drop  100  times  per  minute.  The  blocks  themselves  wrere  not 
monolithic,  but  were  divided,  the  type  of  construction  being  the 
usual  one  with  battery-posts  going  down  beside  the  blocks  and 
setting  on  short  wooden  streak  sills.  The  monolithic  type  of  block,, 
however,  in  which  the  mortar  foundation  for  the  stamp-mill,  regard- 
less of  the  number  of  stamps,  is  in  one  piece  and  flush  all  along  the 
top  and  having  the  battery-posts  setting  in  cast  iron  shoes,  is 
preferable.  In  the  case  cited,  each  block  contained  6%  cu.  yd.  The 
concrete  was  mixed  in  nine  batches,  the  first  eight  in  the  proportion 
of  12  cu.  ft.  of  broken  rock,  9  cu.  ft.  of  sand,  and  3  cu.  ft.  of  cement. 
The  ninth  batch,  forming  the  top,  was  slightly  richer  and  was  mixed 
in  proportion  of  12  cu.  ft.  of  broken  rock,  9  cu.  ft.  of  sand,  and  4 
cu.  ft.  of  cement.  For  reinforcing,  old  wire  cable  was  used,  it  being 
wrapped  around  the  mortar  foundation  bolts  for  each  batch  of  con- 
crete. Cost  was  made  up  as  follows : 

Cement,  55^  bbl.,  cost  delivered $296 

Handling  sand  and  stone 16 

Labor:  mason  8  days,  helper  28V,  days. 115 

Total .- $427 

Average  cost  of  each  block,  $53.38. 

(Note. — Sand  and  broken  rock  were  available  at  the  millsite  without 
charge.) 

Had  wooden  blocks  been  used,  the  cost  under  the  same  circum- 
stances would  have  been  as  follows : 

Lumber,  13  M.  ft.,  cost  delivered $481 

Planing  and  setting 200 

Total $681 

Average  cost  of  each  block,  $85.10. 


224  COST   OF    CONSTRUCTING   STAMP-MILLS 

For  the  second  case,  the  data  following  cover  mortar-blocks  for  a 
100-stamp  mill,  which  is  considered  to  be  one  of  the  best,  if  not  the 
best,  built  mills  in  the  United  States,  everything  being  built  and 
designed  with  the  idea  of  absolute  permanency. 

A  2-horse  team  at  $8.50  per  day  hauled  1  yd.  of  broken  rock  or 
sand  per  load.  A  4-horse  team  at  $14  per  day  hauled  3  yd.  of  broken 
rock  or  sand  per  load.  Eight  loads  in  either  case  constituted  a  day's 
work.  Proportions  used  for  concrete  mixture  were  1  part  cement, 
3.6  parts  sand,  3.67  parts  broken  rock.  The  battery-blocks  contained 
a  total  of  108  yd.  and  cost  $11.82  per  yard,  the  cost  being  made  up 
as  follows : 

Cement $  5.03 

Rock    1.06 

Rock  sand   0.67 

Pit  sand   0.45 

Labor  1.32 

Forms    2.76 

Engineering  and  superintending   0.15 

Reinforcing   0.38 

Total  cost  per  yard  $11.82 

Average  cost  of  each  block,  $63.83. 

The  third  case  covers  South  African  practice,  the  proportions 
used  being  22^2  cu.  ft.  of  2-in.  broken  rock,  7  cu.  ft.  of  %-in.  broken 
rock,  13  cu.  ft.  of  washed  sand,  and  1%  bbl.  of  cement,  making  1  yd. 
of  concrete.  For  the  last  2  ft.  from  the  top,  1%  bbl.  of  cement  was 
used,  the  other  proportion  remaining  the  same. 

UNFORESEEN  CONTINGENCIES.— This  is  an  item  for  which  no 
arbitrary  method  of  figuring  can  be  given,  but  which,  nevertheless, 
forms  an  essential  point  to  be  considered  in  making  up  an  estimate. 
The  unforeseen  always  happens,  and,  incidentally,  invariably  adds  to 
construction  costs.  The  estimator  must  make  an  allowance  to  cover 
the  unexpected  happening,  according  to  the  situation  on  the  ground 
in  each  particular  case.  When  mill  construction  commences  late  in 
the  season,  allowance  should  be  made  for  increased  cost  of  working 
in  stormy  weather.  An  early  rainstorm  plays  havoc  all  around,  holds 
up  freight  teams,  damages  material  not  under  cover,  keeps  men 
from  their  work  in  the  open,  and  in  other  ways  increases  costs.  The 
matter  of  systematic  handling  of  shipments  and  material  has  already 
been  mentioned,  and  figures  given  for  construction  costs  have  been 
based  upon  the  intelligent  and  systematic  handling  of  all  work. 

By  way  of  illustration  of  adverse  conditions,  take  the  case  of 
figures  given  on  framing  mill  buildings,  $25  per  M  board-feet.  As- 


UNFORESEEN    COSTS  225 

sume  that  the  wagon-road  terminates  at  the  bottom  of  a  hill  and 
that  the  lumber  and  material  has  to  be  carried  up  the  hill  to  the  mill- 
site  for  a  distance  of  500  ft. ;  1000  ft.  of  dry  lumber  weighs  approxi- 
mately 3250  Ib. ;  one  man  could  handle  about  100  Ib.  by  hand  and 
carry  it  up  a  20°  slope  at  the  rate  of  50  ft.  per  minute;  20  minutes 
would  be  consumed  on  a  round  trip,  and  counting  the  time  lost  by 
resting,  etc.,  two  trips  per  hour  would  be  about  the  average  for  an 
8-hour  day.  The  cost,  therefore,  of  getting  the  lumber  to  the  mill- 
site  after  the  teams  had  discharged  their  load  would  be  about  $6  per 
M  ft.,  which  is  about  25%  increase  in  the  total  amount  allowed  for 
framing  and  erecting;  and  if  such  a  condition  as  outlined  should 
exist,  25%  would  have  to  be  added  to  the  estimated  total  cost  of 
framing  to  cover  this  contingency.  The  same  condition  would 
obtain  should  the  situation  on  the  ground  prevent  the  machinery 
from  being  hauled  any  closer  to  the  millsite,  and,  as  the  figures  given 
do  not  cover  any  such  unusual  contingency,  it  is  obvious  that  a 
careful  study  of  local  conditions  must  be  made  in  each  individual 
case  to  arrive  at  a  reasonably  close  estimate  as  to  what  the  extra 
cost  will  be  to  cover  the  handling  of  the  material  on  the  ground  as 
an  item  separate  and  apart  from  the  cost  of  construction  and 
erection. 

On  small  mills  up  to  20  stamps  in  size,  the  amount  of  material  to 
be  handled  would  hardly  justify  the  purchase  of  an  elaborate  outfit 
of  construction  tools  and  apparatus,  such  as  power-operated  der- 
ricks. Therefore  appliances  for  lifting  machinery  and  building  ma- 
terial in  general  would  consist  of  the  usual  block  and  tackle,  gin 
pole,  a  good  hand-winch,  chain-block,  timber  dollies,  and  rollers. 
Everything  would  have  to  be  man-handled  from  the  time  it  is 
dumped  off  the  teamster's  wagon  to  the  time  when  the  mill  is  ready 
to  start  operating. 


INDEX 


A 


Page. 
Acid  on  mercury..  107,  108,  138,  140 

plates 138,  141,  142 

Aerial  tramway 11 

Air-compressor  in  mill 180 

Amalgam,  amount  of  gold  in. . .   152 

cleaning 144,  148 

nature  and  kinds  of 107 

retorting  150 

silver    139,  142 

sodium 139,  141,  143,  152,  163 

squeezer    145 

stealing  177 

Amalgamated  gold  pan 145,  168 

Amalgamation    105 

after  heavy  stamps 95 

away  from  mortar 136 

chemicals  in   140 

dry  and  wet 

116,  120,  124,  139,  144 

feeding  mercury 112,  1?2 

in  cyanide  solution.  127,  170,  173 

inside 34,  109,  110,  126,  176 

loss  of  gold  in 161 

loss  of  gold  in  sulphide 162 

on  apron-plate    

116,  118,  124,  126,  131 

on  inside  plates  ...109,  110,  113 

on  sluice-plate    134 

on  splash  and  lip  plates.  114,  146 

outside    125 

principles  of 109,  116 

secondary 172 

test 167 

tools  for  120 

water  required  128 

Amalgamator,  patent 135,  163 

Anchor  bolts  of  mortar 30 

Annealing  graphite  crucible...   152 

stem  54 

Anvil,  iron,  for  mortar  block..     31 
Apron-plate,    amalgamation    in 

cyanide  solution  on 

127,  170,  173 

amalgamation  on 

116,  118,  124,  126,  131 

away  from  mortar 136 

clean-up  of 118,  125,  146 

construction  of 132 

cyanide   on 131,  138,  140,  143 

dressing  the...  118,  124,  126,  131 

drops  in 132 

fall  of  129 

hard  or  stained   142 

preparation  for  use 138 

scouring  of   130 

shaking  132 

silvered  v.  raw  copper..  137,  139 
Arrangement  of  batteries 191 


E 


Page. 

Babbitting  cam-shaft  box ...  62,  63 

Back-knee  battery-frame  24 

Barrel,  clean-up   148 

Batea 149 

Battery-frame 24,  26 

post,  bed-plate  for 32 

pulley,  sectionalized   201 

Belt-tightener   25 

Bin,  arrangement  of 12,  19 

Blake  crusher   14,  202 

Block,  mortar.     See  mortar-block. 

Boiler-setting,  cost  of 222 

Bosshead    44 

fastening  stem  in 56 

iron  v.  steel 45 

repairing 44 

sectionalized   200 

Box,   cam-shaft    62,  63 

distributing...  ..36,   95,  115,  134 

Brass-wire  screen 80 

Breakage  of  stem  and  cam-shaft 

27,  32,  53-56,  61,  194 

Breaker.     See  crusher. 

Bullion,  cleaning 156 

melting  153 

mold 155 

sampling 156 

Buying  a  mill 206 


Cam   50 

design  of   51 

right  and   left-hand 50 

self-tightening   65,     67 

stick    68 

Camming 48,     56 

Cam-shaft 61 

box    62,     63 

box,  babbitting   ' 62,     63 

breakage    27,  32,  61,  194 

changing 64 

collar   for    51,     63 

for  5-stamp  batteries. 51,  63,  194 

hollow  200 

iron  v.   steel 61 

manufacture    194 

sectionalized    200 

Challenge  feeder   69 

Change-room     183 

Changing  cam-shaft   64 

stem 58 

Chemicals  on  plates  140 

Chilean  mill    172,  175,  196 

Choked   mortar 44,  56,  85,  113 

Chuck-block   39,  98,  110 

plate  98,  110,  113 

Clamp  for  setting  tappet 49,     50 


228 


INDEX 


Page. 

Cleaning  amalgam  144,  148 

bullion   bars    156 

Clean-up,  apron-plate.  .118,  125,  146 

barrel    148 

inside  plates   Ill 

pan  149 

room    183 

splash  and  lip-plates   146 

the  general   146 

Collar  for  cam-shaft 51,     63 

Concentration,  crushing  for  ...     97 

Concrete  floor 183 

cost  of : . . .   221 

Concrete  mortar-block.    See  mortar- 
block. 

Construction  costs  of  stamp-mill  211 

Copper  plate,  raw 137,  139 

silvered    137,  139 

Cost  of   boiler-setting    222 

concrete  floor   221 

constructing  stamp-mills  . . .   211 

grading  and  excavating 220 

hardware    216 

lumber    215 

machinery  and  its  erection.   213 

mortar-block    223 

stamp-mill    196 

walls  and  foundations 220 

Counterbore    of    tappet 46 

Crucible,  graphite   152 

treatment  of  discarded 156 

Crusher,  arrangement  of   15 

Blake  v.  gyratory 14,  202 

feeder  for   18 

solid  v.   the  sectional-frame 
Blake   15,  16,  202 

Crushing  for  concentration....     97 

in  cyanide  solution    

81,  127,  165,  171,  173 

in    cyanide     solution,     lime 

encrustation   81,     85 

principles  of  stamp   86 

Crystallization     of     stem     and 

cam-s.haft   53,  61,  195 

Cupping  of  shoe  and  die 42,     52 

Cyanidation,    amalgamation    in 

solution  127,  170,  173 

banking  tailing  for    187 

crushing  in  solution  . . .  .170,  173 

general    169,  171,  178 

mercury  in    127 

Cyanide  on  plates.  131,  138,  140,  143 
mercury. .  .107,  108,  127,  131, 
138,  140 

Cyanide  solution,  amalgamation 

in    127,  170,  173 

crushing  in 81,  85,  127, 

.    165,  170,  173 


Design  of  cam   . . . 
mill    . 


51 

,167,  174,  207 


Page. 

tappet  46,     52 

Die 40 

care  of   42 

cupping  of    42,     52 

false  38 

placing  in  mortar    39,     42 

steel  v.  iron   40 

Discharge,  height  of. 34,  40,  97,  111 
Distributing  box  ...36,  95,  115,  134 
Double-discharge  mortar  ...36,  102 

Dressing  apron-plate    

118,  124,  126,  131 

apron-plate,  the  initial 138 

inside  plates  112 

lip  and  splash-plates    115 

Drop,  adjusting  height  of 60 

height  required    87 

in  apron  table    132 

influence  of  higher  drop  on 

tonnage  89 

order  of    65 

speed  of  88 

Dry  amalgamation 116,  124,  139 

Dynamite,  use  of 43,     59 


Electro-magnet    in    rock-break- 
ing        18 

Emery  wheel  in  mill  47 

Excavating,  cost  of  220 


Fall  of  apron-plate  129 

False  die   38 

shoe  for  increasing  weight. 

92,  200 

Farm  made  of  tailing 188 

Fatigue  of  stem  and  cam-shaft 

54,  61,  195 

Feeder  for  mortar    69 

rock-breaker    18 

Feeding  mercury    112,  122 

the  mortar   98,  112 

Fine-grinding   86,  169,  173,  175 

Finger   jack    68 

Five-stamp  cam-shaft  ...51,  63,  194 

Float  gold  161,  162 

Floor,    concrete    183 

concrete,  cost  of   221 

Floured  mercury    108,  127 

Fluxes  in  bullion  melting 153 

Foundations,  cost  of   220 

Frame  of  battery   24,     26 

Frenier  sand  pump 185 

Front-knee  battery-frame   26 


Gasoline    engine,    loss    of    effi- 
ciency       213 


Gib,  tappet 


.46,     47 


INDEX 


229 


Page. 
Gilpin  County,  Colo.,  practice.. 

9,  52,  97,  162,  164 

Goldfield  Consolidated  mill.. 30,  121 
Gold  from  old  slag,  screens,  etc.  156 
Gold  in  amalgamating  plates. . 

138,  139 

Grade  of  apron-plate  129 

Grading,  cost  of 220 

Graphite  crucible  152 

treatment  of  discarded 156 

Grinding  pan  or  mill..  164,  172,  175 

Grizzly  15,  22 

Grouting  concrete  mortar-block  30 

Guide,  stem  55,  67 

Gyratory  crusher  14,  202 


Hard  amalgamating  plate 142 

Hearing,   loss  of   in   mill 185 

Heavy   stamp    90,  94,  195 

amalgamation  after   95 

Height  of  discharge.. 34,  40,  97,  111 

drop,  adjusting 60 

drop,  influence   on  tonnage.     89 

drop,  required 87 

Hollow   cam-shaft    200 

Homestake  mill   123 

Homestake  mortar    . .  .     35 


Increasing  size  of  mill 22,  175 

weight  of  stamp  92,  200 

Individual   stamp    101,  126 

Inside  amalgamation   

34,  109,  110,  126,  176 

plates   109,  110 

Iron  for  bosshead   45 

cam-shaft    61 

shoe   and   die    40 

stem  55 

Iron  mortar-block  anvil    31 


Key,    tappet 


,46,  47,  50 


Launder,  grade  of    186 

Law  of  millsite  location   13 

Lime  encrustation  from  cyaxiide 

solution    ..81,  85 

Liner  for  mortar   34,  38 

Line-shaft    25 

Lip-plate    114,  146 

Location  of  mill 11,  210 

Loss  of  gold  in  amalgamation.  161 

hearing   185 

mercury    127 

Lumber,  cost  of  215 


Page. 

Machinery,  cost  of   213 

manufacturers    207 

sectionalized    198 

Management  of  mill    181 

Matte  in  melting    154 

Melting  bullion  and  fluxes 153 

Mercury  and  acid.  107,  108,  138,  140 

and    cyanide    solution 

...107,  108,  127,  131,  138,  140 

care  of   108 

feeding  112,  122 

floured    and    sickened. .  .108,  127 

impure    108 

loss  of  127 

properties    of    107 

salivation   by    125 

trap    135 

Mesh,  definition  of  75 

of  perforated  screens 75 

Mill,  buying  a   206 

Chilean  172,  175,  196 

cost  of  construction   211 

design  of   167,  174,  207 

grinding  164,  172,  175 

location  of   11,  210 

loss  of  hearing  in  185 

management    181 

records    181 

talking  in    184 

tests 165 

sampling   69,  169 

Milling  systems   170 

Millmen   and   mill   crews 176 

Millsite,  law  on  location  of...  13 

Mortar    34 

anchor  bolts  for 30 

choked    44,  56,  85,  113 

double-discharge   36,  102 

Homestake   35 

feeding  the  98,  112 

liner  for   34,  38 

open-front    36,39,  59 

rapid-crushing    34 

repairing    37 

rubber  sheet  beneath  ......  31 

sectionalized 38,  198 

splash  and  wave  98,  110 

wood  in  98,  156 

Mortar-block    27 

anchor  bolts  of    30 

concrete 27,  56 

cost   of    223 

grouting  concrete    30 

iron  anvil   for    31 

wood    27,  32,  56 

Mold  for  bullion  melting  155 


N 


Nevada   Hills   mill    115 

North  Star  mill   .117 


230 


INDEX 


Page. 

Open-front  mortar 36,  39,     59 

Order  of  drop  65 

Ore-bin    12,  18-22 

Outside  amalgamation  125 

Overstamping   161,  162,  164 


Painting  interior  of  mill   13 

Pan,  clean-up    149 

grinding    164,  172 

Perforated  or  plate  screen .  72-75,     81 
Plate.     See   apron,   lip,   splash, 
and    inside    plates,    and 
amalgamation. 

Pond,   tailing    186 

Power    required    88,     99 

table   of    100 

Pulley,  battery,  sectionalized. . .  201 

Pumping  tailing   185 

Purchasing  a  mill 206 


Quicksilver. 


Q 

See  mercury. 


Raw  copper  plate  137,  139 

Records  in  mills  181 

Retaining  walls,  cost  of 220 

Retort   150 

Retorting  amalgam    150 

Rock-breaker.     See   crusher. 
Room,  clean-up  and  change....   183 

Rotation   of   stamp    48,     52 

Round  v.  slotted-opening  screens 

74,     81 

Rubber  sheet  beneath  mortar.     31 

Rusty   gold    97,  161,  163 

Russia  iron  screen 73,     81 


S 


Salivation    125 

Sampling  bullion  156 

from  feeder  69,  169 

tailing 170 

Scouring  of  apron-plate 130 

chuck-block  plate  Ill,  113 

Screen  72 

brass-wire  80 

care  of  82 

frame 83 

mesh  of  75 

perforated  or  plate. .  .72-75,  81 
round  v.  slotted-opening.  74,  81 

Russia  iron  73,  81 

size,  table  of  perforated...  75 

standard  testing  77 

tinned  iron  73,  81 

Ton-Cap  78,  81 


Page. 

test - 165 

treatment  of  discarded   ....   156 

woven-wire    75-80,     81 

Secondary  amalgamation    172 

Sectionalized  battery-pulley  ...   201 

bosshead 200 

cam-shaft   200 

machinery   198 

mortar   38,  198 

stem 200 

Self-tightening    cam    65,     67 

Settler,  water  187 

Setting  tappet    48 

Shaking  plate  132 

Shoe   40,     42 

coming  loose 43,  44,     56 

cupping  of    42,     52 

false,  for  increasing  weight. 

92,  200 

putting  on   43 

removing    43 

steel  v.  iron    40 

wedges  for   43,     44 

Sickened  mercury    108,  127 

Silver  amalgam    139,  142 

Silvered  plate    137,  139 

Sizing  test    164,  165 

Slag   in   melting    154 

treatment  of  old   156 

Slime,  definition  of    165 

Sliming    86,  169,  173,  175 

Slipping  tappet    47,  48,     70 

Slotted  v.  round-opening  screen 

74,     81 

Sluice-plate    134 

Sodium  amalgam    

139,  141,  143,  152,  163 

Solution,  cyanide.     See  cyanide 
and  cyanidation. 

Speed  of  drop    88 

Splash  board   112,  114 

mortar   98,  110 

plate   114,  146 

Squeezing  amalgam    145 

Stains  on  plate 142 

Stamphead.     See  bosshead. 

Stamp,   individual    101,126 

heavy  90,  94,  195 

Stealing  amalgam   177 

Steel  for  bosshead    45 

cam-shaft   61 

shoe  and  die 40 

stem 55 

Stem    53 

annealing 54 

breakage    27,  32,  53-56 

changing 58 

fastening  in  bosshead 56 

guide    55,     67 

sectionalized    200 

steel  v.  iron   55 

Sweating  plate    125,  139 

Systems  of  milling    170 


INDEX 


231 


Page. 

Table,  apron,  construction  of. .   132 
of  data  on  stamp  parts. .  .92,     94 

of  power  required 100 

of  size  of  perforated  screens     75 

of  testing  screens  77 

Tail-box 135 

Tailing  disposal  13 

handling 185 

impounding  186 

made  into  garden  188 

sampling    170 

Talking  in  mill   184 

Tappet    46,     52 

clamp  for  setting 49,     50 

counterbore   46 

gib  46,     47 

Key 46,  47,     50 

setting 48 

slipping 47,  48,     70 

Test,  amalgamation   167 

mill    165 

sizing   164,  165 

Testing  screen,  standard 77 

Tinned-iron  screen  73,     81 

Ton-Cap  screen  78,     81 


Page. 

Tools  for  amalgamation   120 

Trap,  mercury   135 

Treadwell  mill   119 

Treasure-box 135,  145 

Trommel 18 

Tube-milling    86,169,172,175 

Twirling  of  stamp  48,     52 

w 

Walls,  retaining,  cost  of 220 

Wave  mortar  98,  110 

Water,  amount  in  amalgamation  128 

amount  in  stamping 85 

temperature    in    amalgama- 
tion     130 

settling  for  re-use  187 

supply    84 

Wedges  for  shoe    43,     44 

Weight  of  stamp   90,     94 

increasing  92,  200 

Wet  amalgamation   

116,  120,  139,  144 

Wood  in  mortar   98,  156 

Wood    mortar-block.  .27,  32,  56,  223 
Woven-wire  screen   75-80,     81 


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